Trailer Brake Controller Shows Voltage on Blue Wire without Brake Pedal Pressed

Updated 07/26/2013 | Published 07/24/2013

Question:

Hello I have a 95 Ford 350 Diesel and my trailer brake control is a Drawtite Activator II. I am having trouble with my horse trailers brakes. The blue wire shows a constant 8 volts which increase to twelve when brakes are manually applied. Is this wire supposed to be hot or is the controller bad.

asked by: Stephen I

Expert Reply:

If the blue output wire is showing power when it should not be then that indicates that the controller is bad and will need to be replaced. But to test it properly you will need to sever the blue wire a few inches from the back of the controller. Then use your tester on the end coming out of the brake controller. If it shows power without the manual override or brake pedal being pressed then the control is bad and will need to be replaced.

If it works like it is supposed to then there is a short elsewhere that is going to the blue output wire. Usually what causes this is corrosion in the trailer connector. Examine the vehicle and trailer side connectors for corrosion on the pins and at the backs of the connectors where the wires attach.

There could also be a problem with the brake magnets or wiring. Examine the wiring and make sure there are no nicks with exposed wire touching metal. Also make sure the ground wires are attached to clean and corrosion free bare metal surfaces. Next inspect the magnets and if you can see the copper windings coming through then the magnets will need to be replaced.

You can further test the magnets by following the FAQ article I have linked for you. I have also linked an FAQ on troubleshooting brake controllers.

expert reply by: Michael H