Attached is a scan of the later Mk1 Escort braking system showing the "Brake pressure differential valve and switch".
If there is failure in either the front or rear brakes the piston within the pressure differential valve moves from its normal central position to either end of the unit operating the electrical switch which in turn lights the warning lamp in the car.
Also attached is a scan of the fascia panel showing two round holes one for the cigarette lighter and the other I believe for the brake failure warning light.
Phil
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