New Trailer LED Tail Lights Do Not Light Up with Running lights on 2011 Lexus IS 250  

Question:

Expert Reply:

It sounds like there could be a ground problem. A weak ground could cause this issue. Different vehicles also have different power capabilities so testing with another vehicle does not always indicate where the problem is.

What you will want to do is test the vehicle without the trailer connected. You are going to need a meter to test the voltage on the trailer wiring harness on your Lexus. If you need a meter we have # PT89ZR. First, test the running light wire going into the converter box on the wiring harness from the vehicle. It is the brown wire. It should show approximately 12 volts when the running lights are on.

If it does not then there is some issue with the vehicle wiring that you will need to have checked out. If it does show the proper power then move on to the brown wire on the output side of the converter. If there is a significant drop in voltage or no voltage then there is something wrong inside the converter and the wiring harness will need to be replaced.

If there is the proper voltage coming out of the converter to the 4-Way then the issue is on the trailer. Make sure both the vehicle side and trailer side connectors are clean and free of corrosion. Make sure that the main trailer connector ground and the grounds for all of the lights are connected to clean and corrosion free bare metal surfaces.

If the trailer has a tilt bed, folding tongue, or aluminum frame all of those things could cause a ground interruption. Running jumper grounds from the lights to the main trailer connector ground can help. The same goes if you have added a plastic license plate holder between a ground and the trailer frame.

I have included some links that should also help you troubleshoot.

expert reply by: Michael H

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