Troubleshooting Unknown Powered Tail Light Converter on 2001 BMW X5

Question:

Bought and installed the powered trailer light converter for my 2001 BMW X5 that was specified for my vehicle. When I have my running lights on the brake lights come on also. The reason being the brake light on the vehicle gets a little voltage when the running lights are on because both lights light up when the running lights are on. When I apply the brake the brake light gets brighter. As a result the converter is reading the initial low voltage from the brake wire as if the brake is being engaged. I thought it was the purpose of the converter to recognize the difference in the voltage from running light and brake light. In the day time without the headlights on it works fine. At night with the headlights on I get constant brake lights on the trailer. Another option is to connect the brake wire from the converter to brake wire only dedicated to the brake, which is the third upper brake light. Its an LED so I dont know if it would have enough power. Please advise.

asked by: Jon C

Expert Reply:

It would help to know what powered tail light converter you have. Some are specified for LED use and some are not. The use of the improper converter can absolutely cause the issue. If you have the proper converter, it sounds like it has a bad ground. The powered converters capture the signal from the brake and turn signals as well as the running lights and don't pull power from your vehicle so the differences in power with headlights on or off.

If you have the TekonshaZCI Circuit Protected Vehicle Wiring Harness w/ 4-Pole Flat Trailer Connector and Installation Kit # 119250KIT, which is what I recommend for your vehicle, then if you have the two wire tail light system then the brake wire needs to be grounded. If you have the 3 wire system then you will obviously connect the brake wire to the brake wire on the tail light using the quick-splice connector included. If you have a two wire system and wanted to splice into that third brake light you can, but I don't recommend it as you can simply ground that brake wire and it will work as intended.

expert reply by: Jason S