Trailer Lights Work On Another Truck But Not On My Truck  

Question:

Expert Reply:

If the trailer seems to work fine on another truck, it sounds like the issue might be in the tow package wiring on your truck.

First, make sure that the 7-Way is wired how you want it. Simply use a circuit tester # PTW2993 and test the functions of the various pins. I have a diagram showing the terminals inside the 7-way and what function each one of the terminals serve. For example, if a prong is used for the turn signal function, you would have a friend engage the turn signal in the cab of the vehicle while you test the prong for power. If you find that the plug is not getting power correctly, or if it is only getting power on certain prongs, you will need to move the search backward, into the vehicle harness to determine where the problem is actually starting.

Next, I would check that the ground connection is good and clean as well. It needs to be grounded to bare metal. If this checks out, the problem is on the wiring itself. If you follow the wires from the backside of the 7-way, there is another connector that the trailer harness plugs into. Use your circuit tester or part # 40376 to test this connector. You should clean both connections at this location as well. If the problem is on the truck side at this point then there is a wiring issue further into the truck and you'll need to inspect the wiring by tracking it throughout. If all checks out fine here, the problem is on the harness and you can replace it.

On the trailer side, some of the wires may be touching each other. You may want to check the wiring for any damaged sections and repair as needed.

expert reply by: Timothy G

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