Malfunctioning Tail Lights on a Re-Wired Trailer with Tail Light Kit TL29BK

Expert Reply:

The first step we take is isolating the problem to either the vehicle or the trailer. The best way to do this is with a circuit tester like, part # 3808. The first thing to do is check the vehicle trailer connector. I assume it is a 4-Way. You would take a the circuit tester, and clip it to the exposed pin on your vehicle connector. This exposed pin should be the ground wire, usually white.

With the probe end of the tester, check the other 3 pins. The brown wire should come on when you turn on the headlights. Yellow should come on with brakes and left turn. The green pin should come on with brakes and right turn. If all these function properly, the vehicle is fine, and the problem is on the trailer. If they do not function properly, the problem is on the vehicle, which I will talk about later on.

If the connector checks out and you determine the problem is the trailer, the first things I would check are the ground connections. Each light should be grounded to the trailer frame. The lights in kit # TL29BK are stud grounded. Meaning that the studs on the lights used to attach them to the trailer act as the ground points. Make sure these studs have direct contact with metal. Paint and rust can insulate these connections. Make sure you have the right wires going into the right connection points on the backs of the lights.

If the connector on the vehicle was not working properly, start tracing wires from the connector to the vehicle. Check for nicks, frayed connections or pinched wires. If you have a Modulite or converter on your trailer connector it is possible that the box has gone bad and in that case you would need to replace it. Feel free to write back and tell me the year, make and model of your vehicle and I can help you find parts if you need to replace them.

Let me know if you have checked all these things and what you found. I will do my best to help you find a solution.

expert reply by: Patrick B