Brake Controller Doesn't Work
Published 08/23/2023
Question:
I have a 2003 GMC 3500 with a Reese trailer brake controller. Im not sure the model of it but it has 4 wires going to the board near the brake pedal and plugs in there. My trailer brakes arent working. When I check the voltage on the trailer brake wire in the back of the truck it says about 2.5 volts and then when I hit the brakes it will go up to a little over 4 volts. When I plug the trailer in Ive tried 2 different trailers It shows 0 volts. The trailer brake wire doesnt have any continuity to any other wire or ground. Every light on the trailer also works as it should. Could this be a failing controller or is there something Im missing? Thanks
asked by: Jake
Helpful Expert Reply:
Thank you very much for your purchase directly from etrailer.com of your Reese brake controller. I'm not certain what the issue is but can offer you some troubleshooting steps. First, You will need to find out if the issue is on the brake controller, your GMC, or trailer. To test the brake controller, sever the blue wire a couple inches from the back of your controller. Then use a circuit to test the end of the blue wire coming out of the controller. It should only have power when you apply the manual override; if it shows power at idle then there is an issue with the controller and it will need to be replaced.
If the controller tests fine, reconnect the blue wire and move on to the truck side trailer connector. Often, corrosion or dirt may be the cause of a short in a trailer connector. Check the plug to see if there is any type of corrosion built up that may be hampering its functionality.
You will also want to test the brake output pin on the 7-way socket; it should only show power with the manual override. If it shows power any other time then there is a short somewhere between the connector and the brake controller you will need to find.
If the truck side checks out then it could be the wiring to the brake magnets or possibly the magnets themselves. Inspect the power wires to the magnets and look for wires that may be pinched or otherwise damaged and fix as necessary. You'll also need to make sure the ground wires are attached to bare metal surfaces and free of any paint, dirt or corrosion.
You'll want to visually inspect the magnets; if you can see the copper windings coming through the magnets will need to be replaced. To test the magnets use Multimeter # PT89ZR and follow the help article I have linked to guide you.
Product Page this Question was Asked From
Digital Multimeter with 42" Long Test Leads - LED Display
- Electrical Tools
- Testers
- Multimeter
- Yellow
- Performance Tool
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