[snoskiguy]

I have a left brake light malfunction. I installed trailer lights on that harness and they worked great. I used a trailer with regular lights not LED and now the left brake light does not work.
There is no melting at the harness.
The bulb is good.
I can put 12V to the wire and the bulb lights up as well as the interior lights when the battery is unplugged. (no burned wires)
I have tested the wire and there is no voltage when the brake pedal is depressed.
What controls the left brake light different than the right? Do I need to test my LCM or is there a fuse somewhere for just the left? Did I overload the circuit with trailer lights and burn something?

[328iX]

Possibly check for a fuse? But I highly doubt it's on it's own circuit.


I'd say either the lcm, or get a high level scanner and see if there's any faults.

There is also the brake pedal switch but then again that would affect all rear lights

[snoskiguy]

Where is the LCM or is the the ECM? Trunk on the right hand side? That's where I traced the wire to.

[Billfitz]

Originally Posted by snoskiguy

What controls the left brake light different than the right?

I can't say exactly, but they are separately controlled. I know this from having coded my lights to LED, and there are separate coding entry lines not only for the left and right brake lights but also for the inner (trunk lid) and outer lights. All the rear lighting is controlled by the REM, rear electronics module, so the fault may lie there.

[snoskiguy]

So I bought a used rear BCM or ECM and the light worked again but now my trunk glass wont open. I'm guessing it came from an F30 not F31. Now off to a shop to try to fix my ECM.
For future reference, if anyone installs trailer lights you have to use LEDs only or but the adapter that is powered. to convert your lights from 5 wire to 4.