I have spent several hours trying to identify a fault on my BMW compact. It failed the MOT on an LED brake light not working. Tested for 12v at the light and neither voltage or earth present. Led works if you apply a voltage to it. So I spent an age running a fresh feed from the brake light cluster. Only problem is when I connect the other brake light into circuit the LED goes out. It seems to need more current than the circuit will supply with both bulbs and led connected. Only solution without dismantling the car to find the fault would be to put a relay in the circuit. Any help would be appreciated.
IIRC a high level stop light not working isn't a failure even if fitted as standard the tester has to assume that it isn't wired up . It used to be at one time if it wasn't visible then it wasn't tested , if it was and didn't work then it was a failure.
sounds like a dodgy earth,chec for grot/rust etc around earth terminals
quote:
Originally posted by rusty nuts
IIRC a high level stop light not working isn't a failure even if fitted as standard the tester has to assume that it isn't wired up . It used to be at one time if it wasn't visible then it wasn't tested , if it was and didn't work then it was a failure.
Bulb failure warning via CAN bus throws a hissy if the resistance of the bulbs is wrong.
You need to track down where the break in the wiring is.
[Edited on 24/3/12 by britishtrident]
Thanks for the replies, I will have another look at it in the morning. Thanks Henry.
Tell them you disconnected it. The wording in the manual states:
Additional stop lamps fitted and connected must be tested. Where extra lamps are fitted and there is doubt as to whether they are connected, the
benefit of this doubt should be given to the presenter.