Troubleshooting Trailer Turn Lights that Stop Working When Running Lights Are On

Question:

I need help trying to figure out why every time the running lights are on the trailer and I press the break and the lights go out also When we turn on the left blinker the left one works when we turn on the right blinker it doesnt work and it does it on the left hand side of the trailer

asked by: Ryan

Expert Reply:

The trailer lighting problems you describe both sound like they are caused by a bad ground connection. A weak trailer wiring harness ground may allow some light functions to work normally while others do not. Problems usually show up when the running lights are turned on, since they pull power continuously, unlike brake and turn lights which are on only briefly.

You can check the main wiring harness grounds on both the vehicle and trailer, making sure both are firmly attached to a clean bare metal surface free of grease, rust and dirt. You can either clean off the existing grounding points or more the ground wire to new spots that provide the bare metal connection required to allow them to pass their full power.

Once you get your grounds in good order you can protect them with an application of dielectric grease like # 11755 which will help prevent moisture and dirt from interfering with your trailer light signals. This grease can also be used on all wiring connectors.

expert reply by: Adam R