Troubleshooting LED Trailer Lights Not Working When Vehicle Headlights Are Turned On

Question:

I have a trailer with LED lights on it. when hooked up to my truck the blinkers and brakes work with the headlights off. When I turn the headlights on, the running lights work but no blinkers or brake lights anymore. I hooked the truck up to other trailers and the lights work fine on others so I think the truck is fine, Any ideas how to get the brakes and turn signals to work with the running lights on? I have a 2004 GMC sierra 1500

asked by: Chad

Expert Reply:

The problem you are having with the lights on your trailer not working is normally related to a ground issue. The running lights will have a continuous draw when on and when you turn on the turn signals or brakes cannot supply enough current. You can start by using a circuit tester like part # PTW2993 and make sure all of the functions are working on the trailer connector. Have someone sit in the driver seat and run through the functions while you test the trailer connector pins.

Ground wire malfunctions can cause all kind of problems including some light functions working while others do not.

You will need to inspect the trailer ground wire that is normally white to make sure it is attached to a clean bare metal surface. Check for corrosion on the trailer connector pins and clean if needed. If the lights are grounded through the mounting hardware, make sure they have a good connection. If a separate wire is used to ground the lights on the trailer, make sure they are attached to a clean bare metal surface on the trailer.

expert reply by: Jeffrey L