Trailer Brakes Stay On and are Humming When Trailer is Connected to Tow Vehicle

Updated 09/26/2012 | Published 09/25/2012

Question:

I have a holden jackeroo 2000 se trubo desiel I have a problem with the brakes staying on slightly all the time on the float when contected to car you can hear a humming noise behind the wheels. when stopped.

asked by: Sharilyn K

Expert Reply:

The humming that you are hearing behind the wheels are the brake magnets being activated. There are a couple different reasons why the brakes are receiving power when the brakes are not being activated.

The first thing that I would check is the brake output wire (blue wire) coming from the brake controller because this will be the easiest and fastest thing to check. You will want to sever the blue wire about 6 inches back from the brake controller and use a circuit tester to see if the brake controller is sending power back to the brakes.

If the brake controller is constantly sending a signal to the trailer connector, then the red wire from the brake controller could be connected to the wrong stop light switch wire or the brake controller is bad and needs to be replaced. The red wire from the brake controller should be connected to the cold side of the stoplight switch which is the wire that only has a signal when the brake pedal is pressed.

If the brake controller is not sending a signal back to the trailer, then the brake wires on the trailer may be contacting the 12 volt power circuit somewhere on the trailer or at the trailer connector. I recommend checking the wiring for any pinched or frayed wires that could be causing a short or allowing two circuits to touch each other. If there is any corrosion or bent pins on the trailer connector, then the connector may need to be replaced. I would also recommend checking the ground connections for the brakes and the trailer connector.

You may also want to test your brake magnets to ensure they are functioning properly. I have attached an article detailing how to test the brake magnets on a trailer.

I have attached a wiring article and a brake controller FAQ article for you to review that should help when troubleshooting this issue.

expert reply by: John H