Troubleshooting Wiring Harness on a 2001 BMW X5 Where Brake Lights Wont Work with Running Lights

Question:

I have your TEKONSHA trailer wiring kit for my 2001 BMW X5. Very easy to install and everything works except the brake lights when the running lights are on. The red brake light wire is connected to the brake black/brown wire that has 2 voltages. The brake lights work if running lights are off. How do I get the brake light to work with the running lights? The module should put out a highet voltage to make the brake lights brighter than the runnung lights. Any help would be appreciated. Thank you!

asked by: B

Expert Reply:

Multiplex wiring like on your 2001 BMW X5 can get pretty confusing. A lot of times there are multiple wires that have multiple functions so it's best to test every wire for each function. I've linked a video of the # 119250KIT wiring harness being installed on a 2013 X5 and you can see where the installer finds two wires each have both the brake and the running lights signals on them. However, the voltage is different one having higher voltage for the brakes and the other a higher voltage for running.

Both wires need to be connected to the harness to operate the function that has the higher voltage. My guess is you've only connected the red wire to one of these and not the brown wire (per the instructions for a vehicle labeled as "BT") and your running lights work at one voltage and the brake lights at the other voltage, but they won't work together.

If you've connected both wires and this doesn't solve your problem let me know how you have each wire of the harness connected, by function, and we'll keep troubleshooting.

expert reply by: Charles S