Installing Brake Controller On 2004 GMC Sierra With Tow Package

Question:

I have a 2004 GMC full size Sierra truck, factory wired round 7 flat pin connector.... is this factory wired for elect trailer brakes? will it power a trailers elec brakes, or a controller or more wiring needed? Also, the running lights work, but no brake lights or turn signals at the plug, are there fuses for this in the truck? fuses specific to trailer lights? any info appreciated...

asked by: Mike T

Expert Reply:

Your 2004 Sierra is factory wired for brakes, but you will need a brake controller to actuate them.

I would recommend a proportional controller, like the Tekonsha Prodigy P2, part # 90885. A proportional controller uses an accelerometer to determine how quickly the tow vehicle is braking, and will send the appropriate amount of voltage to the trailer brakes so that the trailer brakes at the same rate as the tow vehicle. The result is more predictable and safe braking.

In addition to the controller, you would need a wiring adapter, part # 3015-P. One end of the adapter would plug into the rear of the Prodigy P2, the other end would plug into the brake control connector located under the dash. To find the connector, locate the black junction box on the firewall behind the emergency brake pedal. Remove the black cover. The adapter will plug into the second slot from the left in the top row (see provided link).

If you have tested the pins at the 7-way connector, and are not getting signal for brake lights or turn signals, checking the fuses would be a good place to start. The fuses that manage the tow package circuits are located in the power distribution box located under the hood on the drivers side inside fender. There should be a legend on the underside of the lid that shows which fuse serves which circuit.

If the fuses check out OK, check the pins on the trailer connector for corrosion. If you see any green or white corrosion on the pins, it is likely that the corrosion has spread to the interior of the connector and is preventing the signal from getting through. You can check this by unplugging the harness from the rear of the connector and using a circuit tester like part # PTW2993 on the harness itself.