Troubleshooting Trailer Wiring that Doesnt Work Consistently When Running Lights are On

Updated 05/09/2018 | Published 05/07/2018

Question:

I just bought a 2003 sunnybrook 2850 5Th wheel, and just got back from our first trip over this past weekend. While we were headed out I noticed all of my lights were not working properly. All of my running lights are working normal. As long as my running/tail lights are not on, everything works, but if my running lights are and i press my brakes, my right brake light will not work, but my left will left and right looking at the back of the camper also only my right blinker will work. While my running lights are off, the lights work properly. Also I noticed, when the running lights are on one of the tail lights are brighter than the other, the right light is brighter than the left. again left and right looking at the back of the camper. I replaced the right tail light completely over the weekend too, but still having the same problem. I have a 7-way plug in the bed of my truck, and the factory plug on the bumper, and I have the same problem with it plugged into either plug.

asked by: Hunter G

Expert Reply:

Try improving the connection of the main ground wire of the trailer wiring harness. Make sure it is attached to a clean metal surface. Or you can run all of the trailer wires back to the main ground. This is actually the ideal solution. But you can also check the current grounds for the lights to make sure they are making a solid connection to a clean metal surface.

What you described is the classic insufficient ground scenario so finding a way to improve the grounds will fix the problem. When the running lights are on you are drawing the most amperage through the trailer wiring so if you have a weak ground that will be the variable that you'll see problems with.

expert reply by: Jameson C