Troubleshooting a Brake Controller on a 2005 GMC 2500

Question:

i have a 2005 gmc 2500 and i just put a new trailer brake controller in there and wireing from the controller to the computer in the truck. all my lights work but no brakes what do you think the problem could be?

asked by: Brian

Expert Reply:

The problem could be a number of things, but if you do a little troubleshooting you should be able to determine what the problem is. If you are using a plug n play harness you will need to make sure you are using part # 3015-P.

You also may not have all of the wires connected under your hood, check out the FAQ article I attached that shows how do this.

You will want to confirm that you have the wires of the controller attached in the correct manner.

The blue wire is the brake output circuit and will be run to the 7-way.
The black wire is the 12 volt circuit wire that will be run through a 30 amp circuit breaker to the vehicle battery.
The white wire is the ground wire and will be attached to the negative side of battery.
The red wire will be run to the brake switch signal that only sees voltage when the brakes are applied.

On your vehicle the first thing I would check is the brake output circuit on the brake controller for voltage when the manual override lever is pulled. I would use a Circuit Tester # 3808 for this. If there is voltage here then you have ruled out the controller as the problem.

Next, I would start at the rear of the vehicle with a # PTW2993 and have a friend activate the manual override of the brake controller and check for voltage on the brake output circuit. If there is not voltage there you will want to check the back of the connector and look for loose wiring or corrosion and fix as necessary.