Trailer Turn Signals and Brake Lights Not Fully Functional Connected to 2004 Chevy Silverado  

Question:

Expert Reply:

Since the trailer lights work fine on a different vehicle, the likely issue is on the truck. Most likely there is a dirty or corroded trailer connector causing the issue but I would still not rule out a ground problem on the trailer.

On the vehicle, start by making sure the connector is clean and free of corrosion. Also check where the wires attach in the back if it is a 4 and 7-Way or if using an adapter. If you are using an adapter it could be at fault as well.

After cleaning up the trailer connector on the truck, use a circuit tester like # PTW2979 if you need one to test the connector while someone runs through the lighting functions in the truck. If it checks out fine with the tester move on to testing the adapter if using one. Plug it in and use the tester again. If it does not work properly then the issue is inside the adapter and a new one should be used.

If not using an adapter and the signals are not correct make sure the main ground is secured and use the vehicle owners manual to check on any fuses or relays related to the tow package wiring, just in case one of them is on the fritz.

If the vehicle checks out fine then make sure that the trailer side connector is also clean and free of corrosion inside and out. Then make sure the main trailer connector ground and the grounds for all of the lights are attached to clean and corrosion free bare metal surfaces.

If the trailer frame is aluminum, has a tilt bed, or folding tongue, running jumper grounds from the lights to the main trailer connector ground can help. Having a plastic license plate between a light and the trailer frame can also cause some issues. I have included a couple of links that may also help.

expert reply by: Michael H

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