Troubleshooting Electric Trailer Brake System on Trailer Towed by Chevy 2500 Series Truck


Trailer brakes on trailer towed by Chevy 2500 p/u are not working. All systems check out ok. Now what?

Expert Reply:

Discovering why the trailer brakes are not getting power will be a process of elimination. I am not aware of what you have and have not checked, so I will describe the whole troubleshoot process.

Start with the brake controller itself. Is it properly adjusted and leveled (if necessary) according to the instructions? Is it getting power? To determine if the controller is receiving power, you can use a circuit tester like part # 40376 on the black wire that feeds the controller to ensure power is reaching the controller. Next, check the red brake controller wire with the tester. This wire should show current when the brake pedal is pressed. Activate the manual brake switch on the controller while testing the blue controller wire. Voltage should show when the switch is activated.

Have the final connections under the hood been completed? Check out the FAQ articles I have linked to, which will show how to complete the final connections under the hood if necessary. One FAQ applies to 1999-2007 Classic-body models, the other applies to 2007 New body-Present models.

Now, move back to the trailer connector at the rear of the vehicle. Make sure the socket on the vehicle and the connector on the trailer are undamaged. Look for green or white corrosion on the pins and sockets of the connectors. If you see any corrosion, it is possible that the corrosion has spread to the interior of the connector and is preventing the signal from getting through to the trailer. Replace connector if necessary.

If the connectors are in good condition, have a helper activate the manual brake switch on the controller, while you use the circuit tester on the brake output pin on the trailer connector. The pin in the 5:00 position is the brake output. If you do not show any power at this pin, then there is a break somewhere in the wire between the brake controller and the trailer connector. Check that the blue wire is securely attached at the rear of the connector. You can trace the blue wire back toward the front of the vehicle, looking for breaks in the wire. If you cannot trace the wire the whole way back to inspect it, you might need to replace the wire entirely. This would be done by taking the appropriate length of 10 gauge wire like part # 10-1-1 and running it from the blue wire exiting the controller through the firewall and engine compartment, and under the vehicle to connect to the trailer connector.

Next plug the trailer in to the vehicle. Test the brake output wire right before it connects to the brake magnets. Once again, have a helper activate the manual brake lever while testing.

There are some other issues that might be causing your problem. If the trailer brakes will operate with the manual switch, but not when the truck brakes are applied, check the CHMSL fuse in the fuse box under the hood. The lid to the fuse box will have a legend that will help you locate the fuse.

Your trailer brakes might simply need adjusting. If you click on the provided video link, and fast forward to the 4:45 minute mark, you can see a demonstration of the procedure to adjust your trailer brakes.

Your brake magnets might be worn to the point where they are no longer effective. Pull one of the brake drums off, and look at the face of the brake magnet that rides against the inside of the brake drum. If the magnet is worn to the point where the copper windings inside the magnet are visible, the magnet should be replaced.

expert reply by:
Michael L

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