Troubleshooting No Power at Trailer Wiring Harness on a 1996 GMC Sierra With Factory Wiring

Updated 07/20/2010 | Published 07/19/2010

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Twist-in, 7-Pole, RV-Style Trailer Connector for Chevy and GMC Vehicles - Vehicle End

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Hook Probe Circuit Tester

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Question:

I have a 1996 Sierra with a factory tow package. It has a seven pin and a flat four pin connector. Neither one has power for my boat trailer. I checked the wires/connections for the trailer with a car battery and everything from the connector back is fine.I have checked all the fuses and everything looks O.K. It was working fine last year and I havent done anything different. My owners manual for the truck says there is an in line fuse somewhere near the fuse block under the hood, but I cant find it. Any suggestions? Thank you.

asked by: Klaus H

Expert Reply:

It sounds as if there may be a fuse blown in the under hood fuse box. Remove the cover to the power distribution box under the hood and check the tow package fuses to be sure they are in good working order, if not this is most likely the problem.

The 1996 Sierra did not come with a pre-wired 7-way connector but the wiring was ran to a point behind the rear bumper. As far as I can tell all of the tow package fuses are under the hood in the power distribution box fuse panel. I have not heard of an inline fuse near the fuse block on the 1996 Sierra Trucks.

Another thing that is often a problem with the 7-Way and 4-Way connectors is that corrosion forms in the connector causing a short circuit situation. Check the connector inside and out for white or green corrosion that could be causing the connector not to work properly.

If neither of these remedies solves the issue, you will need to use a circuit tester, item # PTW2993 if needed, and start testing the trailer wiring at the rear of the vehicle and work your way forward until you find the source of the problem, which may be a cut, pinched or frayed wire causing a short to ground.

expert reply by: Robert G