Tracking Down Wiring Problem on Trailer Towed by 2003 GMC Sierra  

Question:

Expert Reply:

Having the right and left turn signals flashing at the same time indicates a ground problem. Make sure the ground connection on the trailer is secure and not corroded. The trailer connector will usually have a white wire leading from it that grounds somewhere on the trailer frame, usually on the trailer tongue. The trailer lamps will ground to the trailer frame in one of two ways, either through their attachment studs being in direct contact with the trailer frame or by a separate ground wire. All these connections need to be snug and free of rust.

Showing a constant 12-volts on the right turn pin of the trailer connector would most likely indicate a short circuit from a damaged or corroded trailer connector. I am assuming your Sierra has the OEM 7-way trailer connector, in which case you can confirm that the connector is the problem by unplugging it from the wiring harness that feeds it. Use a circuit tester like part # PTW2993 to test the pins on the plug feeding the trailer connector. One pin should show 12-volts for the accessory power supply, but there should be no power on any of the other pins unless one of the lighting functions is activated. If you do not show voltage on more than one pin, then the trailer connector is faulty and should be replaced. If your 7-way is the OEM type that twists into a hole in the bumper or a bracket, part # PK11916 would be a good replacement.

If your testing shows 12-volts on more than one circuit, then the problem lies somewhere in your tow package wiring, and having your mechanic or dealer find or repair the problem is suggested.

expert reply by: Mike L

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