Trailer Light Not Working and Wiring Harness Show No Power on 2002 Toyota Tundra

Question:

One of my trailer lights is not working properly and I have determined that the pin for that light from the truck wiring harness does not have power. The turn signals work and there is nothing wrong with the trailer light. Is there a small fuse just for that light or what?

asked by: Rodney

Expert Reply:

First, what I recommend is checking the converter box in the trailer wiring, # 118378, to determine if it is the harness or the truck that is the problem. Use a circuit tester like # PTW2993 if needed to test the wires going into the converter box from the truck.

If the signals are correct going into the box, you know that the truck is not the problem. Then test the wires coming out of the converter. If the signals are all correct coming out of the converter, the problem is somewhere on the trailer. If the signals are not correct coming out of the converter box then the converter is bad and it will need to be replaced.

If you find that the signals going in and coming out are working fine, the problem is most likely a bad ground on the trailer. You will need to start by making sure the trailer and vehicle side 4-Way connectors are clean and free of corrosion. Then make sure the main ground for the trailer is connected to a clean metal surface on the trailer frame.

From there you can check the ground at the offending light to make sure it is also grounded to a clean and corrosion free bare metal surface.

I do not think it is a fuse or relay on the truck but you can always check the owners manual to find the location of any fuses related to trailer wiring to see if they are blown.

expert reply by: Michael H