Trailer Lights are Not Working on a Boat Trailer Towed by a 2007 Nissan Frontier with Tow Package

Question:

I have a 2007 Frontier with a pre-wired tow connection. I bought the OEM 4 flat harness from this site and have used it on a trailer with a wishbone 4 way harness. I just bought a boat and it has the same wishbone 4 way harness on its trailer but for some reason none of the lights work except for the right brake light. Although when I bought it the previous owner had it hooked up to his truck and all the lights worked. I tried reconnecting the ground to the trailer but it did nothing. I have also checked the fuses and they are good. Is there anything I am missing or do I need a different harness for my truck? Thank you.

asked by: Aaron

Expert Reply:

To rule out the wiring harness on your 2007 Nissan Frontier as the problem, you can test it using a circuit tester like # PTW2993 if needed. Test the pins on the 4-Way end to make sure all functions are working properly. If they are then that indicates an issue on the trailer side. If they are not, then you could have a faulty wiring harness.

The # C59496 is actually not the recommended harness for your truck, though it could be used. For a 2007 Nissan Frontier with factory tow package, you would use # 118263 which looks like what you bought. Make sure that the relays related to the tow package are in place and functioning. Use the owner's manual to find the location of the relays. Since the other trailer you towed did have working lights, it is probably not the harness on the truck.

Assuming it is the trailer, take a look at the trailer connector. If there is corrosion and/or dirt on the pins, clean it out. You have already checked the main ground but just make sure it is attached to a clean and corrosion free bare metal surface on the trailer.

Next, do the same check with the taillights. All grounds should be attached to clean and corrosion free surfaces on the trailer frame.

Make sure that the boat trailer harness is configured the same way as your 4-Way. Having a different configuration would cause strange things to happen like running lights blinking with a turn signal as an example.

If the boat trailer has a surge coupler, check to see if it has an electric reverse lockout. The connector will have a 5th pin. If so, you would need an adapter, # 20036, to activate the electric lockout.