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How to Repair Electric Trailer Brakes

by Jeffrey Caldwell

Electric trailer brake systems utilize a magnet to spread the brake shoes against the brake drum, which slows the trailer down. In most cases problems with electric trailer brakes occur either because of corrosion in the trailer connector or a break on the wiring between the connector and the brakes themselves. In rare cases the magnets inside the drum brakes can fail and need to be replaced.

Testing the Trailer Connector

Open the trailer connector. In most cases this will be done by removing a small flathead screw on the side of the connector and sliding the outer cover back.

Locate the wire that controls the electric brakes. In most cases this will be the blue wire.

Plug the trailer connector into the tow vehicle connector and have an assistant press the brake pedal.

Attach a 12-volt test light's ground clip to a bare metal portion of the trailer's frame.

Touch the probe on the test light to the screw where the blue wire connects to the trailer connector.

If the test light does not light up, the connector is faulty. Replace the connector, following the instructions provided with the new connector.

Testing the Electric Brake Wiring

If the test light illuminates, that means the trailer connector is in working order and there could be a break or fault in the wiring between the connector and the electric brakes themselves.

Reassemble the trailer connector and connect it to the tow vehicle.

Have an assistant depress the brake pedal.

Locate the wire that controls the electric brake where it enters the drum backing plate at each wheel.Connect the ground clip on the test light to the trailer's frame and use the probe to pierce the insulation on the wire at each wheel.

If the test light fails to illuminate, there is a break or fault in the wiring somewhere between the wheel and the trailer connector.

Examine the wiring; look for breaks in the wire as well as deep cuts in the insulation. Repair and replace any wires as needed.

If the test light illuminates but the trailer brakes fail to engage, the magnet inside the brake drum is defective and will need replaced.

Removing the Brake Drum Magnet

Lower the front of the trailer.

Place jack stands underneath the frame of the trailer at the rear.

Raise the front of the trailer enough to lift the wheels off the ground. Then remove the wheel and tire.

Remove the grease cap on the center of the hub. Then remove the cotter pin and castle nut. Remove the brake drum. The outer wheel bearing will come off with it; be careful not to damage it.

Examine the brake shoes. Trailer brake designs vary by manufacture but in general the magnet will be attached to one of the brake shoes. You will need to remove this shoe to disconnect the magnet. Draw a picture or take a photo of the brake shoes before you take them apart to aid in reassembly.

Remove the springs that connect the brake shoe to the brake drum backing plate at the top of the backing plate. Remove the self adjuster and spring at the bottom of the backing plate. Remove the pin and spring clip that attaches the brake shoe to the backing plate.

Remove the magnet from the brake shoe. Cut the wires connected to the magnet as close to the magnet as possible.

Installing the Brake Drum Magnet

Connect the wires on the new brake drum magnet to the wires removed from the old magnet, using barrel crimp connectors. Connect the magnet to the brake shoe.

Reinstall the pin and spring clip that connects the brake shoe to the backing plate, and reinstall the self adjuster and spring. Reinstall the spring that connects the brake shoe to the brake backing plate at the top of the backing plate.

Reinstall the brake drum and wheel bearing.

Reinstall the castle nut. Turn the wheel as you are tightening the nut. Don't tighten the castle nut so much that it binds the wheel.

Install a new cotter pin.

Reinstall the grease cap in the hub.

Reinstall the wheel and tire.


  • While you have the brake drums off the trailer, check the thickness of the brake shoes and replace as necessary.


  • Always support a lifted trailer with jack stands placed underneath the frame. Never use cinder or wood blocks. Failing to do so could cause injury or death.

Items you will need

About the Author

Jeffrey Caldwell has been a freelance writer for over five months and has published over 250 articles on websites like eHow and Caldwell writes articles on a wide range of topics including travel, camping and automotive mechanics. He has a Bachelor of Arts in English from Millersville University.

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