Troubleshooting Trailer Running Lights That Dont Turn On When Lights are On  

Question:

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 suspect that your grounds might be sufficient for activating one of the lights at a time like when you put the battery on the lights individually, but just not enough for all of the lights at the same time. This is why I suspect that the problem is the main ground for the trailer that runs to the trailer frame.

expert reply by: Jameson C

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