Smartscreen connections Smartscreen internals RWTM connections
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.
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 GT and Mk2