Lights on Trailer Only Work When Headlights are Tuned Off  

Question:

Expert Reply:

It sounds like you have a ground issue. When the headlights are on, the highest amperage draw is placed on the system and a faulty ground will show at this time. I would check all of the ground connections on the trailer. First, check the ground at the tongue. Take the ground loose and clean the connection point on the trailer and the wire end. Next, check the trailers taillights. Most taillights are grounded through the mounting bolts to the trailer frame. Make sure the connections are clean and solid. If there is a plastic license plate holder on the left side this may be causing the ground issue and you will need to make sure the mounting bolts are making good contact with the frame. Your taillight brackets could also be connected to the trailer frame with bolts and this connection could be rusted and/or corroded enough to cause a ground issue.

You should be able to find the problem in no time, just by checking the grounds, but if you do not find it then you will need to use a circuit tester, item # PTW2993, to test the wiring on the trailer. Test each circuit and you will find the one that loses power when the headlights are on. Once located run the wire down looking for a pinch, frayed or broken section that could be the problem.

Finally, your vehicle could be one of the few vehicles out there that have a multiplexed system and requires an alternate wiring configuration. Let me know the year, make and model of your vehicle and I will be glad to try to help further if the above recommendations do not solve the issue.

expert reply by: Robert G

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