Troubleshooting Trailer Wiring Where Stoplights/Turn Signals Dont Function

Question:

Parking lights work on the trailer but the turn signals and brake lights do not. Brand new 999t8-br004 harness all fuses are good. 2018 Nissan frontier s king cab its a mystery to me.

asked by: Walter

Expert Reply:

You need to first determine if the problem is the trailer's wiring or the tow vehicle's wiring. You can do this with a circuit tester like part # PTW2993 which you'd use to test each of the pins on the vehicle's 4-way for voltage when the taillight circuits are applied. You also should check to make sure there is no corrosion on the pins of the trailer connectors as well as that's typically what causes the problem you mentioned. It also can be an insufficient ground for the trailer wiring since the brake lights draw a lot of current. You might make sure all of the lights are connected to a clean metal surface and that main ground strap of trailer's 4-way is connected to frame solidly. I attached a help article on trailer wiring for you to check out as well.

expert reply by: Jameson C