Troubleshooting Tow Package Wiring of 2004 Chevy Suburban

Question

Question:

2004 Chevy Suburban with factory install tow package. Bought the vehicle used and to the best of my knowledge, never towed anything. Hooked brake controller up under dash without incident and has power gets the n/c not connected light. Hooking to a trailer I have traditionally pulled with my 99 pickup without issues. Cant get the lights to work. Seven pin plug just like my truck. Does not seem to have power to the plug socket on Suburban. Checked fuses and all seem fine. Pulled a few of the fuses in box within engine compartment and used a tester to see that there is power to the fuse socket. It appears that there is nothing but the wiring harness in between fuse and plug in back but wiring. Just cant seem to see the issue. Help!

asked by: Bob F

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Expert Reply:

Your Suburban has a fuse box under the hood, under the dash, and on the drivers side edge of the instrument panel. Each fuse box has fuses that relate to the towing circuits, see page 5-110 of your owners manual for a listing of the fuse locations.

If the vehicle has never been used for towing before, it is unlikely that all the fuses that protect the tow package circuits have been blown. From what you describe, no power is reaching the plug under the vehicle that your 7-way trailer connector plugs into. First, examine the connector for excessive corrosion or damage. Clean or replace as necessary. Also, check the connection to of the 7-way to the wiring harness it is plugged into. If the connector is not plugged into the socket all the way, it might explain the problems you are experiencing. If the connector is fully plugged in and is in good condition, you can have the dealer or your mechanic look at it, or you can simply bypass the factory tow lighting circuits by installing a tail light converter like part # C59496. The inputs of the converter would tap directly into the wiring harnesses feeding the tail light assemblies. On the output side of the converter, you would remove the 4-pole trailer plug. Next, find the wiring harness that plugs into the back of your 7-way. If you pull back the wire loom, you will see a brown, white, yellow and green wire. Cut each of these wires and connect the like colored wires from the converter to the wires leading to the connector. The converter will also have a wire that needs to be ran to the positive battery terminal.

From what you said in your question, the brake controller is not reading the trailer. This means that the output circuit is not complete between the controller and the trailer connector. It is possible that the same problem that is preventing the lighting inputs from reaching the trailer connectors is also preventing the brake controller output from reaching the trailer connector. I would recommend running your own output to the trailer connector, once again bypassing the factory wiring. Sever the blue wire exiting the rear of the brake controller, and add a length of 10-gauge wire long enough to pass through the firewall, under the vehicle and reach the trailer connector at the rear of the vehicle. The wire will need to connect to the # 2 pin on the trailer connector.

I have linked you to some FAQ articles that you might find helpful.

expert reply by: Mike L

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