Troubleshooting Turn And Brake Trailer Lights Not Working When Running Lights Are On

Question:

I have checked all grounds. Each light is grounded via the case. I disconnected each case one at a time while the running lights were on. after I disconnected the case the light went off at that case. so I know ground is code at each case. also disconnected white trailer ground and all lights went off. when running lights are off break and single lights work lights use to work so I know it is not a power issure or to much current. I am at a loss any ideas

asked by: Michael H

Expert Reply:

The problem you described is many times associated with grounding problems. You said you checked each light, but you will need to see if you the ground for the lights may be causing the problems. The first thing I recommend is to disconnect the trailer from the vehicle. Weak grounds can cause this issue as well. Make sure the ground wires are secured to a clean bare metal surface. If you have an aluminum trailer you will need to run the ground from each light back to the ground at the trailer connector.

Then use a circuit tester like part # PTW2993 and check each pin on the vehicle side connector for function to make sure it is working correctly. If that checks out, hook the trailer back up and check the wiring coming out of the trailer connector to make sure there is power for each function. Any loose grounds wires or corrosion on any of the connectors can cause issues like you are having with the lights.

I have attached links to a couple helpful articles that explain how to troubleshoot and also how the wiring is typically run for a trailer.

If you are still having problems after troubleshooting, let me know what the year, make, and model of your vehicle is as well as the type of trailer you are using, and I will see if we can find a solution that works for you.

expert reply by: Jeffrey L