LED Trailer Taillights Malfunction When Vehicle Headlights Are Activated  

Question:

Expert Reply:

The situation you describe is the classic, dictionary definition of a ground problem, either on the vehicle or the trailer side of the equation.

This is usually caused by one or more ground connections that aren't tight or that have been connected to corroded or dirty metal. You're getting a partial connection, enough for the lamps to function under normal circumstances, but when full power is being drawn through the system (like when the vehicle headlights are turned on) things either stop working or they don't work correctly.

I'd recheck all your ground connections, including the one for the trailer wiring harness where it grounds to the tow vehicle. Make sure they're tight, and that ring terminal for your ground connections is contacting bare metal. I like to sand the area around all my ground connections (about the diameter of a dime) and use a star washer between the ring terminal and the metal you're grounding to. The star washer will bite into the metal, ensuring a good, bomb-proof connection. To protect your connection, give the area a quick shot of rust inhibiting spray paint.

Also, check the inline resistors, and ensure they've been installed according to their manufacturer's instructions. I'll link to a trailer wiring troubleshooting article, and I'll provide a diagram showing how a resistor should be installed.

expert reply by: Mike L

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How to Wire a Load Resistor
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