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Hey now, here's a problem I've not seen posted before. Yesterday just after I started the car I needed to get something from the boot, and when I was at the back I saw that the brake lights were on despite no brake pedal activation. Subsequent investigation revealed: when rear window heater is on (either automatically via ACC or by manual switch) the brake lights come on; when the brake pedal is depressed the brake lights work OK, but the heater indicator on the dashboard also lights up (not as brightly as when the heater is on "properly"); if the rear window heater is on (and therefore all brake lights are also on) and the brake pedal is then depressed then the main brake lights remain on, but the high level light goes out.

I would guess a wiring issue at the back of the car is to blame, however ... for some time I've had water dripping in from the overhead light / switch position and wonder if this water might have found its way into the wiring /switches at the front of the car.

Any views / thoughts?
 

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Odds are that there is a problem with the ground to the rear screen heater. When you turn it on the current finds it's way back through the brake light circuit. Bet it doesn't get very hot either.
 

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It would seem likely that there's some form of earth fault at the back. When you brake, the brake lights earth through the HRW, and when you turn on the HRW, it earths through the brake light circuit, in the absence of the proper earth circuit. I don't understand the brake light going out though!

However, check the earths from both circuits and I expect that you'll find something wrong.
 

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The heater is earthing through the high level brake light so all the brake lights come on. When the brakes are applied the high level lamp now has 12V at both sides of it so no current flows through it and it goes out. Like wise the high level light is earthing through the screen heater making the heater lamp glow.
Seems to me that the earth to the rear hatch and its electrical bits is missing. Check the connections for corrosion.
 
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