Hello everybody I am having issues with the 7 pin trailer lights on my 2006 ford F150 (4 pin works flawlessly). The only thing that works on my 7 pin is the left blinker and left brake lamp. Nothing else works from running lights, right turn signal, right brake lamp, etc.. I have already replaced fuse #10, #36, #42, and still nothing. I even replaced the tow hitch wiring harness with another OEM harness and that did not do the trick. It is not the trailer as it works fine with my other truck. I would appreciate anyone's help. I am out of ideas.

 

Fuses cannot cause this issue. The 4 and 7 pin circuits for the running and the L/R stop/turn lamps are simply spliced together in the harness.

Since we don't know exactly what the " tow hitch wiring harness " that you replaced encompasses, it's not possible to determine if it should or shouldn't have repaired the problem.

 

If the 7-blade plug in your trailer gives power to all the lights, battery, brakes, etc. when you plug it in to another truck's 7-blade receptacle, then the problem is in the wiring of your truck. As project told you, since the 4-blade and 7-blade receptacles are simply wired together at the rear of your truck, the problem is either in that wiring connection or inside the 7-blade receptacle itself. Have you tested for voltage at each of the blades on your truck's 7-blade receptacle? You can get an inexpensive plug in tester that uses lights to check this if you don't want to use a multimeter.

Receptacles and plugs CAN go bad. I had to replace the plug on my trailer last year due to an internal short circuit that kept tripping the circuit breaker in the trailer.

- Jack