Trailer Tail Lights Not Working on a Trailer Towed by a 2008 Nissan Titan

Question:

The brake lights, and turn signals are working when I hook up my trailer. But the tail lights are not working. What relay would control this so I can replace it, the brown or the blue one?

asked by: Nick R

Expert Reply:

The two blue relays are used to activate the turn signals and the brown relay is for the 12-volt circuit. You would need to consult the vehicle owner's manual to determine if there are additional relays, whether under the hood or in the in-cab panel, that control the other functions. Some Nissan vehicles do require an additional relay, obtained from the dealer, to make the trailer wiring harness fully functional.

To determine if the issue is on the truck or trailer what you can do is disconnect the trailer and use a circuit tester like # PTW2993 if needed to test the pins on the trailer connector. If the running light pin is not showing power, then you know the issue is on the truck. But if it is showing power the issue is on the trailer.

Usually, a dirty or corroded trailer connector can cause this problem. Corrosion can also build up behind the connectors on the vehicle or trailer where the wires attach. Also make sure the main trailer connector ground is attached to a clean and corrosion free bare metal surface. Do the same for each of the trailer lights. A bad ground can cause this same issue.

expert reply by: Michael H