I have the same problem as discribed below. 2007 Nissan Frontier -- Trailer running lights stopped working. Brake lights and turn signals still work. Where is the fuse for the trailers running lights. I have factory harness installed by Nissan.

One wire is for the brake/directional filament and the other wire is for the tail light. The fixture should be grounded when it is attached to the bracket. To test which is which (the brown wire is USUALLY the ail light) make sure the fixture is grounded and touch a hot wire to each of the wires coming from the fixture. Watch to see which wire lights up the brighter filament and this is the brake/directional light. The dimmer filament if the tail light. Brakes lights and directional lights are both the same filament. Wen the brakes are applied, both lights are activated. When a direction light is turned on, it simply flashes the brake light filament.

check for signal ground,this is not a metal ground, use a test light or volt meter to see if they at plug before you plug in the trailer, you may need to rewire the trailer.

If the turn signal bulbs are the same as the turn signal bulbs it would indicate the brake light on the left is not working. If the brake lights AND the right turn signal come on it could indicate a wire is getting a cross feed from an improper source. If you are comfortable with electrical systems - If you have a tow package you may want to check the wires to the trailer. Otherwise have it checked by an electrical shop.

First check the fuses. There may be one for trailer running lights. Check also power at the harness. If the brake lights and turn signals are seperate, there has to be a converter from 5 to 4 wire. For the power to feed back to the brake lights it sounds like the vehicle wiring is direct and not using a converter... or one of the bulbs on the trailer is contacting both contacts. Try http://www.etrailer.com/faq-wiring.aspx and maybe get a simple 4 pin tester that plugs into the 4 pin connecter. Hope this helps.

check the relays for the lights, and check the fuse again, make sure the bulbs are all good

Most likely it is the relay which is built into the turn switch. Turn switch will have to be replaced. It is also good idea to replace the flasher as well. Make sure both bulbs are new.

You may be better off checking at dealer, or autoparts store for an adapter harness that goes inline. They simply plug into the harness ahead of all your tailights etc, and make it easier. At most, you may end up having to run a separate wire for brake control.

There should be a 30 AMP mini blade fuse in the fuse box under the hood that you are probably missing. I assume that since you got the relays with the wiring kit, that you got the kit from a Nissan dealer. If that is true, there should be a fuse in the kit also- in a sealed bag that has the "trailer wiring harness owner's manual" in it.


Hope this is helpful!


Nissan Scope Technician- 10+ years experience in Nissan dealership.