Another difference to the later 2-terminal units is how they respond to a failure of a bulb at the corner of the car. From brief exposure to one of these units with one bulb not working the other bulb only makes a very brief flash, barely visible to other road users.

If that wasn't enough there are at least two types of this flasher unit - one for MGBs and one for Triumph TR4 and earlier, and the difference is in how the tell-tale is operated. Helping a pal with the indicators on his TR4 he had bought what he thought was the correct flasher unit ... but the tell-tale was on all the time with the ignition, albeit flashing when the indicators were being used. From what I knew about the Mk1 MGB system I realised that what he had was an MGB unit, which has the additional contacts on the indicator switch so the tell-tale is off when they are not being used. The TR4 only has one tell-tale for both sides, and no extra contacts on the indicator switch, so it needs a flasher unit where the tell-tale contact is not live until the unit starts flashing. Paradoxically it wouldn't matter if the TR4 and earlier unit was used on an MGB, so the question has to be why the MGB had a different one (the MGA apparently had two different systems, one the same as the Triumph and the 1500 which is completely different as it involves flashing the brake lights).

Current replacements can be stocked as GFU101, GFU2101, GFU103, GFU2103, SFB105, FL5, FL54, C16729, 35002, 35003, 35010, 35028, 35028A, RTC3560, UD1511 and probably others! Some of them are for Triumph but will work equally well in the MGB (unlike the other way round). Some Triumph sources report similar problems to the Lucas SFB115 two-pin flasher unit for Mk2 including being a hazard flasher and not an indicator flasher.

Mk2: A simpler system with only Lucar/spade two terminals on the flasher unit - 12v to B (green) and L (light-green/brown) to the indicator switch, and no extra contacts on that switch. The two dash-tell-tales are simply wired in parallel with the bulbs at the corners of the car - one per side, so come on and go off with the corners. These units have the safety feature that as soon as you operate the indicator switch both the corners that side (and the dash tell-tale) light up, and after a pause start flashing off-on-off-on.

A second safety feature is that if one corner fails the other corner and the tell-tale will glow steadily instead of flashing, which is a warning to the driver that they may need to start using hand-signals.

A drawback of this system is that the flasher unit is very sensitive to voltage and current, and with low voltage or increasing resistance from ageing connections and bulbs the flash rate gets slower and slower as well as reducing the brightness of the bulbs, and this is where some have changed to using three-pin electronic flasher units. With these the third terminal is an earth connection, the other two are the same as for the original unit. Many of these (but not all ...) have the same safety features of lighting up straight away and indicating when a corner has failed, except that in the latter case with one corner not working the other corner and the dash tell-tale will flash at double speed. Being electronic they don't suffer from slowing down with falling voltage or increasing resistance issue and give a much more consistent flash rate, BUT ... dimming bulbs from those causes will remain dim. It's a significant exercise to investigate that, and there can be very many small extra resistances throughout the circuit to find and fix, although fixing the greatest resistances first will have the greatest effect.

Current stock replacements are the aforementioned suspect SFB115 as well as SFB114, GFU125, GFU2125, 8FL, 35049. Note some of these may be cylindrical, the can won't fit the original rectangular clip but may come with its own clip. Also that rectangular ones may be double-height but they fit the original clip. Confirm that the packaging or can states '48W' or '50W', and/or '2 x 21W' (may also include '+6w +2w') and NOT '12A', '96W' or '4 x 21W'. Even then when fitted immediately test and confirm that as soon as you operate the indicator switch the lamps light up, then after a short pause start to flash - may well need the engine to be running to flash at an acceptable rate.

That leaves LED bulbs which are whole different world of pain in the indicator flasher unit department.

These operate differently to indicator flashers and are a different construction internally. For a start when you first turn on the hazard switch nothing happens, then they start flashing on-off-on-off. Secondly they are capable of flashing anything from one to four main bulbs (plus side indicators and tell-tales) if for example the vehicle has been in an accident and one or more corners are damaged. Secondly they are relatively insensitive to falling voltage as they may be left operating for some time without the engine running, and flash at a relatively consistent rate. Two-pin devices (like the Mk2 indicator flasher) - 12v to B (brown) and L (light-green/brown) to the hazard switch which links the two sides and connects the flasher unit to them. The flasher switch has two more contacts that are normally closed with the hazards off and these feed fused ignition power (green) to the indicator flasher unit. These contacts disconnect that when the hazards are operated, otherwise if the indicator switch was left operated power from the hazard flasher to the corners of the car could feed back through the indicator switch and the indicator flasher onto the green and white circuits, and hence power the fuel pump and the ignition even with the ignition key in your hand - an obvious safety hazard in the event of damaged fuel lines.

Unfortunately having two spade terminals like the Mk2 indicator flasher unit they can be substituted for each other in error. With a hazard flasher in place of an indicator flasher things will appear to work, but there will be a delay in the corners lighting up when the indicator switch is operated, and there will be no indication of bulb failure. The other way round is more obvious as with an indicator flasher trying to light all four corners there is only the briefest of flash lighting them before they go off again.

With LED bulbs at the corners the standard hazard flasher may work if there is are incandescent bulbs in the tell-tale, but probably not if they are LEDs as well.

Hazard lights were standard on North American spec cars from the start of Mk1 production in 1967, on all V8s, and non-North American 4-cylinder cars from the start of the 1974 model year i.e. the last chrome bumper cars according to the list of detailed changes in Clausager ... or is it? He says in the text that they were also available as an optional extra on home market before that, but that the information available is 'conflicting', and it is. He says the 1973/74 GT brochure for home market cars quotes them as an optional extra, but no mention at all in the 1974 roadster brochure. '1973/74' could be taken to mean both 1973 and 1974 models, but could also be the model that was built during the second part of 1973 and the first part of 1974 which would be the 1974 model built from August 73 at chassis number 328101 (roadster) and 328801 (GT) to September 74 at chassis number 360301 (roadster and 361101 (GT). Elsewhere he says they were 'probably' fitted to all home market cars from the start of the 1974 model year. The Leyland schematics show it for 1974 models but not for 1973 models, in neither case as an option. The Parts Catalogue shows hazard switch BHA5267 being used for RHD chassis number HD5-328801 which is specifically GTs from the start of the 1974 model year, but it doesn't indicate it is an option unlike for fog and spot light switches. Flasher unit ATJ8880 is specified for chassis number 328101 (roadster) and 328801 (GT) i.e. all 1974 model cars and again no indication of being optional. The only clear thing is that all RB cars had them. It may be that when the 1974 model brochures were being produced it got into the GT one but not the roadster one, and by the time it came to build the cars they had decided to fit them to both roadster and GT anyway (why would they fit it to one but not the other?). Who knows, other than looking at actual cars of the period, but even that is fraught.

Brian Wall has said his November 72-built GT has them i.e. a 1973 model built between August 72 and August 73, which raises the possibility that they were an option in 1973. But that could be a mod by a previous owner, possibly with a rewire, it looks like that was the only electrical change between 1973 and 1974 models. If it had been an option the later harness could have been installed on the line as required, or maybe it was on all of them and the switch and flasher unit not provided. In which case there would need to be a dummy 'switch' on the connector to link the two green wires together or the indicators wouldn't work, in which case to add hazards would just be a case of adding the switch and flasher unit to the connections. The option could also have been a sub-harness added to the earlier standard harness, which is what I did.

Adding hazard flashers is not simply a case of tapping into a 12v supply and the wiring to the corners of the car which is easily done. The hazard switch when on has to interrupt the power to the indicator flasher unit for safety reasons. Feasible with a sub-harness as it would be a case of simply removing the 12v feed from the indicator flasher, connecting that to the sub-harness, then connecting another wire in the sub-harness back on the indicator flasher. But if the main harness had provision for optional hazards there would need to be an link (insulated from coming into contact with anything else as it would be part of a bunch of wires not attached to anything i.e. flapping around) between the two green wires going to the switch, removed when the switch was provided.

May 2019: A puzzling problem for Steve Henson-Webb on the MGOC forum. When using his indicators the dash tell-tales worked, but when using the hazards they didn't. The appropriate corners of the car flashed when they should. Unfortunately he didn't mention until later that when using the indicators both tell-tales were flashing, but dimmer than usual, which made things much easier to understand. The problem was the earth wire to both tell-tales had become detached. That meant that when using the indicators the tell-tales were effectively in series to earth via the indicator bulbs on the side of the car that wasn't flashing, so both flash, albeit dimly as each has only 6v instead of 12v. When the hazards are on both tell-tales have 12v on their 'live' sides, but no earths on the other, so neither flashed. The puzzling thing is that it was a 1974 CB, but on Mk2 tin-dash cars (e.g. my 73) there is no earth wire for the indicator tell-tales that I'm aware of, the bulb holder picks that up from the bracket they are pushed in to, which is attached to the back of the dash. He says it happened after fitting a radio, maybe that interrupted the dash earthing somehow, but seems unlikely. Mk1 cars (which didn't have hazards from the factory of course) did use 2-wire indicator bulb-holders as the 12v supply was switched from the flasher unit and the earth supply came from the indicator switch. North American Mk2 with the padded dash, all V8s and all RB cars also have 2-wire indicator bulb-holders as they are mounted in plastic panels so need a wired earth.

The indicators are powered from one of two green (fused ignition) circuits - originally the one in the fusebox. But sometime in 1978 when the ignition relay circuit on RHD cars was modified to add a second in-line fuse between brown/white and green wires under the fusebox, the indicators (and tach, heater fan and GT GRW) were powered from one of these - the one with the thinner wires, the other with thick wires being for the cooling fan. For more information see the ignition schematics. On cars equipped with hazard flashers the green circuit goes via the hazard flasher switch to be connected when the hazards are off, and disconnected when they are on.

By all accounts indicators are the bane of an LBC-ers life. But like all things, they worked when it came out of the factory. If it doesn't work now then there must be a reason (or two or three), so it can be found and fixed.

But first - know the difference between indicator/turn flasher units (they are not relays, strictly speaking they are thermo-switches) and hazard flasher units:

• With indicator flasher units as soon as you operate the switch the lamps should light up, and after a short pause they should start flashing off-on-off-on.
• With hazard flasher units as soon as you operate the switch nothing happens for a short period, then they should start flashing on-off-on-off.

If you substitute an indicator flasher for a hazard flasher it will appear to click at the correct rate but will only send power to the bulbs very briefly, not long enough to fully light them, and may burn-out quickly as they are only designed to flash two 21w bulbs (plus a 5w wing repeater on the 2-pin types) not four. But if you substitute a hazard flasher for a 2-pin indicator flasher it will at first seem to work correctly, unless you notice the sequence (as above) is incorrect. This is a safety hazard, as it delays the lights coming on and hence the warning to road users. So many people these days seem to operate the indicators at the same time as they turn the wheel that the rest of us need all the warning we can get!

There are also 'universal' or 'heavy duty' flasher units that although they may have the correct sequence for indicators i.e. they come on as soon as you operate the switch, don't have the built-in 'bulb failure warning' of the originals. Really when fitting an alternative flasher unit you need to disconnect one corner and confirm that you still get this warning. On original MGB types this warning is that flashing stops altogether, and only one external bulb will be lit. On modern electronic units the remaining bulb should flash at double-speed.

To complicate matter even further there is another type of after-market indicator flasher unit intended for use with after-market LED bulbs, more on those here.

As well as straight-forward disconnections causing non-working bulbs, the 2-pin MGB indicator/turn flasher is very particular about the amount of current it needs to work - it doesn't have to drop very far due to low battery voltage or bad connections before you start to get slow, or non-flashing where the lamps stay lit all the time. Incorrectly rated lamps will cause problems, as will 'tired' bulbs that were originally the correct rating but have become high-resistance internally with age. This is another difference to the Mk1 3-pin flasher units, which even with one bulb disconnected will try to operate and can give a faint click and a very brief flash of the other bulb. It's unfortunate that the change in design that meant they light the lamps immediately the switch is operated, also made them so sensitive to current. But on new cars out of the factory that wouldn't have been a problem, only to us 40 years down the road!

Some suppliers are showing SFB115, GFU2124 or GFU2125 as replacements for ATJ8880, but these are indicator flashers only capable of operating two 21w bulbs, they are not hazard units which need to flash four 21w bulbs. The correct item is SFB130, aka 35053.

1. Cars to chassis number 161086 had a switch with contacts for selecting which dash tell-tale would be lit as well as contacts for controlling which side of the car would be lit. There were three variations on that - the second being to angle the stalk closer to the steering wheel, the third had what Clausager describes as "longer peg for more positive location". Only one replacement switch seems to be available - BHA4628
2. From chassis number 161087 non-North American cars up to chassis number 187169 (roadster) and 187840 (GT) had a switch with a headlamp flasher - BHA4898, except Japan which had a switch without the headlamp flasher - BHA4897.
3. North American Mk2 cars and non-North American cars from chassis number 187170 (1969 model year) up to chassis number 219000 (1970 model year) had a switch with dip/main, headlamp flasher and horn functions - BHA4948
4. From chassis number 219001 (1971 model year) until 410001 (1977 model year) all markets had the horn button back on the steering wheel, 37H8050 for chrome bumper, 37H8101 for RHD rubber bumper and all V8 with legends for function, 37H8523 for LHD with words for functions.
5. For the 1977 model year for the remainder of production the horn button returned to the indicator stalk, AAU4991 for RHD, AAU4995 for USA, AAU4993 for Canada. These act as the mounting plate for wiper switch (AAU4992, AAU4996, AAU4994).

August 2023: Replacing the indicator/lighting/horn stalk on a pal's 78 (indicator contacts not functioning) with a new Lucas-boxed unit the mounting collar on the switch has a tab that is supposed to locate into a cut-out on the column outer. This tab can clearly be seen on the earlier switch (above the legend 'Contact fingers') and prevents the switch assembly from rotating about the column outer as the stalks are operated. Or it should but the tab on this new switch will not go into the cut-out, I think I can feel where it is trying, but is maybe too wide. On a subsequent visit I was determined to resolve this so took the switch off and did a trial fit of the old switch which went straight into the location notch. Took that off and put the new one back on ... and that also went straight into the location notch! Weird.

Cancelling:
For cancelling, cars up to chassis number 187211 (basically 1970 models that began at chassis number 187170 in September/October 1969) had a peg screwed into the column. After that until 1977 the steering column has a clip which is a tight fit but can be slid round to the correct position. For 1977 on a different arrangement was used where the steering wheel itself interfaces directly with the indicator switch.

The inconvenience with the early peg is that the whole column has to be turned in the UJ to get the correct alignment, and then the wheel turned on the column, whereas the clip can just be slid round to the correct position. Both types slide under fingers on the switch and lift them out of the way as you make the turn. With the early type as the wheel is returned the peg catches the metal finger, which lifts up the spring that is holding the stalk to one side, and the stalk should return. June 2015: Note that this type of column inner slides freely in the tube and if removing and refitting or replacing the column as a whole you may have to adjust the position of the outer in its clamp brackets, i.e. slide it up or down relative to the inner, to get the indicator switch in the correct position relative to the cancelling peg, even though the switch position on the tube can be adjusted to some extent. The position of the inner is determined by the U-joint and rack.

I've always had my clips facing the indicator switch with the wheel in the straight-ahead position and that way the wheel only needs a 1/4-turn in order to cancel when the wheel is straightened again. However three people on the MGOC MGB forum stated that their pegs face away from the switch, and the wheel needs to be turned 3/4 before it will cancel the indicators. The 77 and later indicator switch has a collar that is continuously rotated by the wheel and has an identification rib on one side of the collar. If that is facing the switch then again only a 1/4-turn of the wheel is needed before it will cancel as the wheel is straightened. If it faces away from the switch then it needs a 3/4 turn before it will cancel. Obviously off the car it can be positioned anywhere, but having looked at half a dozen suppliers photos they all show the rib facing the switch, so I'm pretty sure that is how they should be on the car. Also checking on my Mercedes A-class that only needs the wheel to be turned 45 degrees to hear the click of the cancelling mechanism (how agricultural ...) which will then cancel the indicators as the wheel is straightened.

On the later type of indicator switch with plastic fingers the cancelling cam engages with the end of the finger and physically pushes the switch back to the central position. The fingers can wear such that the cancelling cam just lifts the fingers up again rather than bearing on them to cancel the switch, as well as the fingers having broken off or the cam being in the wrong place or missing.

Note that the clip-type cancelling cam or striker changed twice - once in June 73 on 4-cylinder cars from BHH254 to BHH1301, and again in September 74 for rubber bumpers to BHH402. This later change was for the full energy-absorbing column and column-stalk mounted OD switch that V8s had always had, but neither column nor switch seem to have changed on 4-cylinder cars in June 73. Roadwarrior says one was taller than the other, but he also says that when that is fitted to the wrong car the problem is that it causes the indicators to cancel as you start making the turn as well as when you straighten up again. But that is a different problem to the one that led up to him making that comment on the MG Enthusiasts Forum - non-cancelling - and may be the same cause but in the other direction i.e. the lower cam fitted where there should be the taller one. I've had to build-up the one on Bee, possibly after I changed the switch but I can't be sure. The V8 with the original switch (not changed by me at any rate) and striker has never been a problem.

February 2020:
I get both cowls off and compare the cams and columns. The upshot is that the V8/RB cam is 'taller', but as well as that the column shaft is wider. So whilst in error the CB cam could perhaps be forced onto the V8/RB shaft it may well not be tall enough to push the indicator switch fingers back. Also whilst the V8/RB cam being taller may operate the CB indicator switch better, it will be a looser fit on the smaller column so may not stay in place. Possibly 'pinch it up' enough to grip, but the curvatures would still be different.

Update September 2007:

June 2018:

Mk2 CB RHD (and LHD without the padded dash) cars have a holder with only one wire to the tell-tale (13H1924), the holder picking up an earth from the bracket on the back of the dash panel. The same MES E10 bulb as above. In front of this bracket is a tube which concentrates the light onto a green plastic lens, which is positioned behind an arrow-shaped cut-out in the dash panel.

  Early padded dash have a unique dash fitting and a two-wire (green/white or green/red and black) claw-type bulb holder similar to Mk1 cars, and takes the same MES E10 bulb.

Later padded-dash, V8s and rubber bumper tin dash have a tubular lens pushed into the front of the dash panel, secured from the back with a spire clip. The bulb holder has two wires, the second providing an earth as the mounting panel is insulated, and pushes into the lens from the back. The bulb is a BA7S (GLB281) i.e. bayonet-type.

From 1977-on with the smaller squarer rocker switch the rear fog-light switch has an internal bulb (LES GLB921 screw fitting) for the tell-tale function showing orange as well as the night-time illumination showing green.

  Apart from that where indicators light but don't flash one side this printable schematic and chart should help you to plot the voltages through your circuits and locate any bad connections. You don't need the engine to be running but it is more realistic if it is from a voltage point of view, and won't flatten the battery (dynamo-equipped car may need a bit of fast idle to extinguish the ignition warning light). If you don't run the engine (saving fuel) then disconnect the coil to prevent it overheating which it almost certainly will do with the ignition left on for a long time (with the exception of some electronic ignition systems). Non-flashing could be due to a failed flasher unit of course as well as bad connections. An ammeter in place of the indicator flasher unit should ideally show 3.5 amps, if it shows 3.2 amps or higher but doesn't flash then the flasher unit is probably faulty. With bad connections a new flasher unit may well start them flashing again, but this can simply be due to its being new and more sensitive, as it 'burns in' they will probably slow and stop again. If you are investigating slow flashers, and they continue to flash slowly, it makes measurements easier if you bridge the two connections on the flasher unit to stop it flashing. See here for the results of the tests on Vee.

  This sensitivity to current was deliberate to give warning to the driver if a corner should have failed, otherwise traffic around you may not realise you are preparing to turn. Modern flashers use electronics (instead of a heated bi-metallic strip) and flash rapidly if one of the main lamps fails and are nowhere near as sensitive to slightly bad connections as the original 2-pin units. Some people fit a modern electronic flasher to their classic car when they get slow flashing from poor connections, not realising that they will still there and causing the lights to be dimmer than they should be. A pal fitted one of these a while ago, but on doing voltage tests for another issue more recently found he was getting less than 8v at each rear light. Whilst fitting an electronic flasher unit to get round 'slow flashing' problems because of bad connections may seem to have done the trick - temporarily, eventually you may have to find and fix the root cause(s), you might as well do it now and get brighter lights. Be aware that some aftermarket types flash at the same rate regardless of current and therefore give no warning of lamp failure, so if you wimp-out and fit an alternative flasher unit disconnect one of the bulbs with it fitted and make sure that the flashing speed changes. If not, you run the risk of being rammed up the back because the person behind had no idea you were going to turn so didn't expect you to slow down. Electronic flasher units have their own problems - or at least people have problems with electronic flashers, as I have known of at least two occasions where the driver was blissfully unaware that because one side flashed at twice the rate of the other it indicated bulb failure, they hadn't even noticed! As Einstein reputedly said "Only two things are infinite - the universe and human stupidity, and I'm not sure about the former." Likewise LED Bulbs have their own issues.

  As mentioned before the indicators circuit is: Battery - starter cable - brown circuit - ignition switch - white circuit - fuse (note 1) - green circuit - hazard flasher switch (note 2) - green circuit (note 3) - indicator flasher - light-green/brown circuit - indicator flasher switch - green/white (RH side) and green/red circuits (LH side) - indicator bulb holder - indicator bulb - indicator bulb holder - body earth (note 4) - battery earth cable. CB cars with twin-6v batteries also have the battery link cable.

Note 1: Later cars have an ignition relay and white/brown circuit between the white circuit and the No. 2 fuse.

Note 2: The indicator flasher is wired via the hazard switch so that it is disconnected when the hazard flashers are turned on, and only works when the hazards are turned off. This prevents the outputs from the hazard and indicator flashers from conflicting with each other, but more importantly prevents the hazards feeding power back through the indicator switch, indicator flasher, green circuit, fusebox and onto the white circuit and so energising the fuel pump and ignition (my thanks to Mark Childers for pointing this out). So don't be tempted to bypass the hazards switch if it is that which is causing your indicators problems.

Note 3: The 'green' circuit from the hazard flasher switch to the indicator flasher should really have its own tracer as it is no longer part of the 'real' green circuit.

Note 4: Rear light clusters on all cars and front indicator/parking light clusters on CB cars have the cluster picking up an earth from their physical fixings to the body. RB front indicators have a wired earth shared with the headlights/front parking lights.

Typical indicators faults can be "They don't work at all" or "They don't work on one side" or "They light but don't flash or flash too slowly" or "They flash but so do other lamps" or "They don't cancel".

  "They don't work at all"

  "They don't work on one side"

  "They light but don't flash or flash too slowly" Updated April 2013

  "They flash but so do other lamps"

  "They don't cancel" Updated September 2007

Note: The indicator flasher is wired via the hazard switch so that it is disconnected when the hazard flashers are turned on, and only works when the hazards are turned off. This prevents the outputs from the hazard and indicator flashers from conflicting with each other, but more importantly prevents the hazards feeding power back through the indicator switch, indicator flasher, green circuit, fusebox and onto the white circuit and so energising the fuel pump and ignition (my thanks to Mark Childers for pointing this out).

These tests should be done with the ignition off, and all wiring connected, except where specified otherwise.

First check for 12v on the brown and light-green/brown terminals of the hazard flasher. Note: North American cars prior to 1972 have a third terminal on the hazard flasher with a light-green/purple wire. From 1972 on this wire was on the hazard switch. This is for the hazards tell-tale and should be ignored in all tests.

July 2018:
Happened to come across an NOS indicator flasher in a red bubble pack for £5.50 on eBay so snapped it up. Ticks faster than either of the units that came with Bee and Vee, and on Bee flashes with the engine stopped, so far so good. However it's noticeably quieter, so a couple of times I've found I've left it on after a turn. September 2020: while testing other aspects of the lighting the indicators have gone back to not flashing with the engine off, just one tick changing from one side to the other as before, proving that there is a 'burn-in' period and they deteriorate slightly for the bulk of their life. Still plenty fast enough with the engine running.

July 2023: Just lately the indicators have been noticeably slower, so I was thinking that perhaps the NOS 8FL above had aged a bit now and was as bad as the others. I still have the after-market ones that were slower than an old FL, tried them and they were no better, in fact one of them kept blowing the fuse because one of the terminals had pushed through the plastic base when I was fitting the spades and was shorting-out internally. That was because when I pulled the spades off the 8FL they didn't seem very tight so I had pinched them up a bit. Went back to the 8FL and with the tighter connections it speeded up significantly, and has remained so.

Note that while modern 3-pin electronic flasher units don't suffer from the slow flashing problem, neither do they warn you of worsening electrical connections that will be resulting in dimming bulbs.

Secondly they will not work correctly with either the original thermal or 'standard' electronic flashers - in the former case both bulbs will light but not flash, in the second case they will flash but very quickly indicating bulb failure. Some vendors supply a load resistor with LED lamps so that the original flasher units (thermal and electronic) flash at the correct rate, but then the 'bulb failure warning' feature in the original flashers will only detect resistor failure, not LED or wiring failure!

You can get indicator flasher units specifically for LED lamps which should flash them at the correct rate - 2-pin and 3-pin where the third pin goes to earth. But again, these do not tell you when a corner has failed and so are equally as unsafe as load resistors with standard flashers, and with some types if you connect more than one filament bulb to them you will burn them out. Also some contain a relay and make an audible click and some do not. April 2018: Out of interest I purchased a 3-pin type advertised as being for 0.02A to 20A so apparently suitable for anything from all-LED to all-filament indicators and hazards. But on all-LED they just flashed once, even though there was a current of 0.9A. It needed an filament tell-tale bulb added to boost the current to about 1.3A before they would flash repeatedly. Ends

A supplier of a 2-pin type claims that they are the units fitted to BMWs (but at only £14 I find that unlikely). Also I'd be surprised if modern cars were allowed to get away with there being no indication of failure as IMO it is a significant safety hazard. On questioning the supplier they defended themselves by saying LED bulbs were much less prone to failure than filament which is correct, but there can still be wiring or connector failure as before which will have the same effect. They defended that by saying failure warning types were being developed but had no date for availability, something I find difficult to believe when they are supposed to be OE units. I've not been able to establish yet whether OE use does or doesn't have failure warning, but recently I was behind a Range Rover with these bulbs which stopped in the middle of the road prior to turning across the traffic without indicating. Cussing the driver under my breath I then noticed as he turned that the side marker was flashing at the correct rate! Which indicates (ho ho) that Land Rover at least may well be fitting these with no failure warning. In theory cars should detect disconnections in the wiring right up to the bulb holder as there is a load resistor inside the 'bulb', but that still won't detect failure of the light emitting elements, and they do fail, especially after-market components.

Note that if you fit LED lamps and the LED indicator flasher unit you will probably need to change the hazard flasher as well. Whilst hazard flashers are designed to flash anything from one to four 21w filament bulbs, they do still need a certain amount of current flowing through them, and the current from even four LEDs can be less than one filament (21 watts i.e. 1.75 amps). My 'standard' hazard flasher will - just about - flash a single 6w filament but it won't flash two 21W-equivalent LEDs.

About the only excuse for fitting LED indicators is they can be left operating for a lot longer in the event of a breakdown or accident without flattening the battery - unless you have installed load resistors at the same time and retained the original flasher unit!

Hazard flashers were standard in the North American market from the start of Mk2 production in late 1967, but not added to other models until the either the 1974 model year or rubber bumpers, it's not entirely clear. Before adding hazard flashers to earlier cars it is vital to understand that the hazard switch must disconnect the standard indicators in some way, otherwise it is possible to have the fuel pump and ignition powered even with the ignition off and the key in your hand, which is obviously a serious safety hazard (pun not intended) especially in the event of a collision. If a hazard circuit is simply added to the indicator wiring then with the hazards turned on and flashing the lights, if the indicator switch should happen to be operated, power will feed backwards through the indicator switch, indicator flasher, onto the green circuit and through the fusebox onto the white circuit. Factory flashers power the indicator flasher unit through the hazard switch in the 'off' position, disconnected when the hazards are turned on, for retro-fitting this reverse current path can be disconnected either with a suitable switch, a relay or blocking diode.

Options are:

• Obtain a factory-style rocker switch and wire it as per factory wiring. This will require diverting the green circuit that feeds the indicator flasher unit as well as connecting to the green/white and green/red lamp circuits, and connecting the new hazard flasher via an in-line fuse to a brown circuit. A good option for UK cars with the earlier style of rocker switches as there is an empty space in the centre console, and could also be used on toggle-switch cars in a supplementary panel.
• Use a generic double-pole double-throw switch with the green/white and green/red wires from the corners of the car connected to the two common terminals, the normally closed contacts connected to the green/white and green/red wires from the indicator switch, and the normally open terminals connected together and to the hazard flasher. Requires diverting both the green/white and green/red circuits which can be done at the bullet connectors between the main and rear harnesses in the engine compartment if you don't want to cut wires.
• Use a generic on/off switch and two relays, one relay tapping into the red/green and red/white wires for the hazards, and the other disconnecting the indicator circuit when the hazards are in. This disconnection can be done where the light-green/brown wire connects to the indicator flasher unit.
• Use a generic on/off switch and diodes to connect the hazard flasher to the green/white and green/red circuits via two diodes, with a third blocking diode in the green circuit feeding the indicator flasher unit.
  Note: Inserting diodes into circuits results in a small volt-drop which means that slightly less voltage will be reaching the lamps. With incandescent bulbs there there will be a small reduction in brightness, it's up to you whether you consider this to be acceptable, MGB indicators are not the brightest to begin with. Note also that diodes can fail, disabling either hazards or indicators, or could cause both sides to flash with the indicators and damaging the indicator flasher (but then so can relays and after-market wiring).
• Hazard flasher conversions are available as after-market add-ons, make sure these do disconnect or block the existing indicator circuit to prevent this reverse current flow. The vendors may have no idea what you are talking about, so always test after fitting by looking for 12v on the white or green wires at the fusebox with the ignition off, hazards on, and indicator switch operated to one side or the other. If the circuit is not blocking this reverse path you will see 12v switching on and off as the hazard flasher unit clicks. It's up to you whether you are happy to use it or send it back. Note that a kit advertised in the MGOC 'Enjoying MG' magazine showed the detail of the connections in the October 2013 issue and did not interrupt the indicator circuit.

There is also the hazard tell-tale to consider. According to the schematics UK cars don't seem to have had these (why would you need one when both the dashboard indicator tell-tales will be flashing anyway?), but North American spec always did. From 1972 this was fed by a light-green/purple wire off one of the contacts of the hazard switch and a 2-wire hazard flasher unit was used. In this case only the first option above can be used, as the tell-tale needs to be isolated from the hazard flasher unit and the indicator wiring when not in use, and only the factory switch (or similar hazard-specific switch) does this. The schematics show that from 1968 to 1971 a 3-wire hazard flasher unit was used, with the third wire feeding the tell-tale, and this type of flasher and tell-tale wiring can be used with any of the options above. 3-wire hazard flashers seem to have been used on a number of British cars of the era, still seemingly available from the likes of Rimmer, Canley Classics and others. Check they are capable of driving at least 4 21w bulbs, they may also be marked 'heavy duty'. Alternatively it may be possible to wire a tell-tale bulb in parallel with the 2-wire hazard flasher i.e. directly to its two terminals. This will flash the tell-tale in anti-phase to the corners of the car instead of in phase as with the factory and 3-terminal options, but should be legally acceptable for inspections.

Finally power to the hazard flasher must come from an always on, fused source. 'Always on' because the hazards need to be available with the ignition off and the key out, fused in case one of the corners of the car is damaged and the lamp holder or wiring is shorting out. Without a fuse this could cause a fire, adding to your woes. Factory cars were wired from the brown circuit via an in-line fuse solely for the hazard flasher, originally in the very inconvenient location of behind the centre console! Whilst it is technically feasible to power it from the purple circuit which is also always on and already fused, as this feeds the horns and other circuits accident damage may have shorted out that wiring elsewhere on the car and blown that fuse. This means that if you are going to the trouble of adding hazard flashers, a separate fuse off a brown wire is really the only sensible option.

Adding to Bee: August 2013
After a pal had his TR6 written off by being rear-ended, just a couple of weeks after completing a two-year restoration to make things even worse, I decide I really need to fit hazards to Bee (Vee has them as standard). The TR6 didn't have them, although in that case I don't think it would have made any difference. The car had broken down on a dual-carriageway, was only half on the carriageway and half on a grass verge next to a crash-barrier, in clear visibility on a straight road just after a roundabout, with my pal back up the road warning people to keep over. Nevertheless this ... chap seemed totally oblivious of both my pal's warning as well as the car, almost hit him, then smacked right into the TR6's off-side rear corner which caused the perpetrator to spin and roll, coming to rest on its side. But anything that might improve visibility of these, by today's standards, small cars has to be of benefit and I decide to fit hazards before going any further with DRLs which a pal and I have been pondering for some time.

August 2023: Checking Bee over prior to an MOT - lights, wipers, washers, horn. Main lights - fine. Hazards - fine. Brake lights - fine. Indicators ... no indicators. I'd only been out in her a couple of days previously and they were fine then. The hazard switch disconnects power from the indicators (as explained above) so flipped the hazard switch on and off again and the indicators worked again. Only installed 10 years using the standard switch as there was a spare position in the centre-console, they are probably only used twice a year - pre-MOT and MOT, so hardly 'worn out'. I tried the switch a few times and most of the time it worked as it should but every now and again if I switched it off slowly the indicators didn't work. Quite co-incidentally a pal I'm helping with his electrics gave me a new hazard switch of the correct type just the other day which he had bought for his car not realising it used a different switch. Fitted that, working again.

I'd had the same thing on Vee's hazards not long after buying her 30 years ago, opened up the switch and it was full of hardened grease. Dug that out and replaced with fresh, worked again and has done ever since. I'm almost certain that is the original switch. Opened up this switch, only a little grease and certainly not hard. Cleaned that out anyway and scraped the contacts (as I had to do with said pal's brand-new main lighting switch straight out of the box) and with a test meter that seems OK now, so has gone in the spares box.

When I restored Bee just over 30 years I replaced all the dash switches as the logos were a bit faded, then some years later the new main lighting switch started getting intermittent. As the logo on that was getting a bit faded I put what was almost certainly the original switch back, and that has worked ever since.

New stuff is rubbish even though it looks exactly the same as the originals.

When you first operate the indicators you won't hear anything - don't panic! It is only when the lights go out on the first click of the flasher that the buzzer will sound, i.e. it operates in anti-phase to the lights. If you find the buzzer too loud you can always wrap a couple of turns of insulating tape or similar round it. However the cheap electronic buzzers make a pretty horrible sound, and even the piezo type can get annoying, so I'm experimenting with something to make a louder clicking noise with my NOS original which although flashing quicker is quieter than the old one ... watch this space!

February 2020: An enquiry on the MGOC forum reminded me that I hadn't updated this. My first thought was to wire a small loudspeaker in series with a capacitor. The theory being that although the impedance of a typical speaker is far too low to wire across the flasher unit and would affect both it and the lamps, adding a capacitor would prevent that but allow to capacitor to 'charge up' and discharge via the speaker each time the flasher contact opened and closed. I used to have a couple of speakers from small transistor radios I messed with decades ago, but couldn't find them. Got one off eBay but it was much smaller than expected and was way too quiet.

Next thought was a solenoid where the ends of the plunger were exposed, and positioned in a box or by a bulkhead the plunger would hit the sides of the box or the bulkhead so making a noise each time it operated and released (in a box) or just on the one stroke (bulkhead). Ordered one of those, but in the meantime I discovered an old GPO electronic sounder with three volume settings. Tried that and like Goldilocks and the three bears one setting was too loud, another wasn't loud enough, but the third setting was just right. It's also quite a melodic sound very different to the harsh 12v buzzer, so that's as far as I went.

The MGOC forum reminded me that I had also seen buzzers for motorcycles, including one type with a delayed response of 20 flashes or so before it started buzzing. Some of these have an additional feature that if you sit there with your brake lights on the buzzer is muted until you release them. As Dave Birkby said - "bizarre". Whilst I can understand car drivers sitting at traffic lights with a foot on the brake (instead of selecting neutral and applying the handbrake ...), do bikers habitually do that? Even though modern bikes light the brake lights from both front and rear brakes? And one motorbike forum was discussing a system where the buzzer only sounded once every ten or so flashes. Both relatively easy using a chain of bistables or JK flip-flops, should you be so inclined - four to give you a count of 8, five for 16.