Right Tail Light Stays On When Trailer is Unhooked from the Vehicle and Trailer Battery is Removed

Question:

I have a strange problem, the right tail light stays on the trailer when my vehicle is unplugged. It started when we moved the trailer with a bobcat and the lights werent even plugged in. The only way I can get it to go off is to take the 12V battery out. Seems strange, any ideas? Thanks

asked by: Joe H

Expert Reply:

It sounds like the power from the trailer battery is somehow reaching the right brake and turn signal circuit. The brake and turn signal circuit on the trailer should not be connected to the trailer battery.

The first step I would take is to check the wire connections inside of the trailer connector. On a 7-way trailer connector, the pin for the 12V battery power is right next to the pin for the right turn and brake signal. If these two wires are touching, then that will explain why your right taillight is constantly receiving power. I have attached a photo showing the inside of a trailer side connector.

If the connections inside of the trailer connector look good and there is no corrosion or wires touching each other, then start at the right taillight with the trailer battery attached and test for the brake and turn signal wire using a circuit tester like part # PTW2993. It will be the only wire with power running through it. Follow that wire toward the front of the trailer looking for any damaged or frayed sections that may be making contact with a circuit that is powered by the trailer battery.

I would also recommend inspecting the rest of the wiring on the trailer just to ensure that there are no other areas that are damaged or that could likely cause problems. I have attached an article on trailer wiring that should help while troubleshooting this issue. If these steps do not help you find the issue, then let me know what you come up with and we can take further troubleshooting steps.

expert reply by: John H