Troubleshooting Low Voltage/Dim LED Trailer Lights from New Harness

Updated 09/29/2014 | Published 09/28/2014

Question:

I recently bought tail lights part #TLL160RK and installed everything as directed. However, the tail light LEDs are very dim and turn signals and brake lights do not function. Using a multi-meter, I tested the voltage coming out of the vehicle adapter for tail lights ~13v and right/left turn signals flashing up to 12v. I then connected the harness for the Optronics kit and saw a significant voltage at the end of the wiring run: tail ~5-6v and turn signals flashing to 5v. I then tested the new wiring harness closer to the vehicle near the tongue where I will put side-lights and get the same voltage readings as at the end of the wiring run. I used the same location on the trailer as ground for all tests. I then check the old wiring harness that I had replaced. Tail lights ~11.5v and turn signals flashing to 10-11v. The old harness is a heavier gauge wire than the new Optronics harness so I went back to the old harness and re-installed. Now that I get more voltage to the lights, the LEDs are definitely brighter not stellar but still no turn signal or brake lights, and no license plate light. How sensitive to voltage are the LED lights? This is taking much longer than it should. Hoping you can help. Vehicle is a 2005 F150.

asked by: Sean B

Expert Reply:

You will need to get at or very near 12 volts in order for the Optronics Trailer Tail Lights part # TLL160RK to illuminate properly. What I would recommend you first do is check the grounds of the trailer and the assemblies themselves.

You want to make sure the main trailer ground is connected to a clean metal surface on the trailer frame. This is the ground strap that runs from the connector on your trailer to the frame.

The ground wires of the assemblies need to be connected to a clean metal surface as well.

I attached an FAQ on troubleshooting trailer wiring for you to check out as well.

expert reply by: Jameson C