Trailer Left Side Running Lights Not Working All Other Lights Work

Updated 06/16/2015 | Published 06/14/2015

Question:

I have the trailer lights wired through a conjunction box to a WesBarg 7-Way, RV-Style Connector w/ 6foot Long Coiled Cable - Trailer End - WG54006-043. the turn and brake lights work. the right side running lights work but not the left.

asked by: Kevin

Expert Reply:

On many trailers the running light wires are jumped from one side to the other on the trailer. This is because there is a single running light wire only ran on one side. A wire would have to be spliced in on the one side, ran to the other side of the trailer, and connected to the running lights.

If using a junction box, the one running light wire from the trailer connector can go to a single terminal and from there you can run separate wires for the running lights on each side of the trailer. So first make sure that there is a wire for the left side running lights.

Another possible cause is a ground issue. Make sure all of the lights are grounded 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.

And finally, if the trailer has a lot of running lights then they could be drawing more power than the system can handle. To test that you can disconnect some of the working lights and see if any of the other lights start working. If so then to draw less power you could switch all the lights to LEDs.

expert reply by: Michael H