Intermittent Wiper Systems

Smartscreen connections    Smartscreen internals    RWTM connections   

Smartscreen connections

Plenty of scoppe for confusion. Three intermittent wipe modules are available - positive earth, positive earth converted to negative earth, and Mk2 and later negative earth, the negative earth module is shown here. Positive earth and 'positive converted to negative' modules do not have spades at 'Wsh' or 'P'. 'Wipe with wash' modules are available for both positive and negative earth and have a spade in the 'Wsh' position:

There are basically three different systems in the MGB depending on whether it is a Mk1 roadster, an Mk1 GT both of which are positive earth, and all Mk2 cars. If you have converted a positive earth car to negative earth there will be two more variations, and if you fit a positive earth module to a Mk1 then convert to negative earth you will have to buy a negative earth module, or remove it and do without.

Mk1 roadster - single speed, original wiring. An earth from the manual switch runs the motor. For basic parking an earth from the park switch under the gearbox cover is wired direct to the motor:

Mk1 roadster with Smartscreen:

Mk1 GT single speed with an improved external parking system wired via the manual switch, original wiring. An earth from the manual switch runs the motor. For parking an earth from the park switch in the motor goes via the manual switch in the Off position back to the motor on 'run' circuit until it is parked:

Mk1 GT with Smartscreen:

All Mk2 2-speed. The manual switch supplies 12v to the slow or fast windings of the motor for running. For parking 12v from the park switch in the motor goes via the manual switch in the Off position back to the motor on the 'slow' circuit until it is parked:

Mk2 with Smartscreen:

For the 'wash/wipe' version connect the 'Wsh' terminal to the light-green/black wire from the column stalk to the washer motor.

Smartscreen internals

Following an enquiry from someone who was investigating the possibilities of making their own version, but couldn't read the lettering on the IC top right, I found the original high-res image and it is '12C508' which is an 8-bit CMOS Microcontroller, loads of hits on Google.

RWTM connections Mk1 roadster, Mk1 GT and Mk2:

Mk1 roadster

Mk1 GT and Mk2

  • Mk1 GT uses red/light-green for its single speed and black/green for parking.
  • Mk2 use red/light green for slow, blue/light-green for fast, and brown/light-green for parking.