Electric Trailer Brakes Stay On when Towed by a 2006 Ford F-150

Question:

I bought a new camper 3 yrs. ago went on trip and did no know ele. brakes had power to them all the time messed up all brakes. Got back to dealer they checked my 2006 f150 and said they needed to put in a horn relay this corrected the problem for two yrs got my camper out to use after winter storage went about 50 miles have the same problem again just enough current going to the trailer brakes to make them drag and over heat. could the problem be with the relay they installed. Also where is the relay located. If the power boost on the brake controller is ran up too high could this cause this problem with current going to the brakes all the time.

asked by: Mitchell

Expert Reply:

First, it is possible that the relay that was installed actually has more than one function as it does seem odd that the horn would be related to trailer brake output. I wonder if the horn stops working too if that relay goes bad. You can consult the owners manual and/or the power distribution box lid for the locations and functions of all fuses/relays.

If adding the relay fixed the issue the first time then it is possible that the relay has gone bad again. They would need to figure out why it keeps going bad but if there is a short due to corrosion or dirt in trailer or vehicle side connectors, that is one possibility. Also check the wiring to the brake magnets for any exposed wiring touching the metal trailer frame.

The brake controller should only send power back when you step on the brakes or use the manual override so as long as it is working properly that should not be the issue. If it is a factory integrated controller they can probably diagnose it at a Ford Service Center.

If it is aftermarket, sever the blue wire a few inches from the back of the controller and use a circuit tester like # PTW2979 if needed to test the end coming from the controller. It should only show power when you apply the manual override. If it shows power and any other time then the controller is bad and will need to be replaced.

Also, if it is an aftermarket controller, make sure it is mounted within the range specified in the instructions and not tilted or turned to the side. To adjust the output level you will want to connect the trailer and take it to a flat surface. Go about 20 miles an hour and apply the manual override. If the brakes lock up adjust the power down. If they do not lock up adjust the power up. You want it set to a point just under brake lock up.

expert reply by: Michael H