Troubleshooting Trailer Taillights that Stop Working When Brake Pedal is Depressed

Question:

left brake light not working with wiring harness attached when brake pedel depress left brake light turns off every thing else works leftturnworking right turnworks tail lights work also right brake light working also.

asked by: Augustine

Expert Reply:

This sounds like a ground issue. Ground problems normally show up when there is more draw on a system such as when you have the running lights on and then use another function like a turn signal or brake light. Make sure that the vehicle side and trailer side connectors are clean and free of corrosion inside and out. The main connector grounds should be attached to clean and corrosion free bare metal surfaces. The light grounds should also be attached to clean and corrosion free bare metal surfaces. If there is anything between a light ground and the metal trailer frame or if the trailer has an aluminum frame, tilt bed, or folding tongue, any of these things can interrupt the ground. Running jumper wires from the light grounds to the main trailer connector ground can help.

I also attached an FAQ on 4-way troubleshooting for you to check out as well.

expert reply by: Jameson C