Yesterday I pulled my boat out of the shop for the first time with my new truck (2005 F150). I can't back up the trailer as the brakes keep locking up. I checked the truck plug, with a light meter, and there is no power at the truck plug when you put the truck in reverse. Reverse is supposed to power a solenoid that keeps the surge disk brakes, on the trailer, from working so you can back up. Any ideas?

 

When you got the truck, the factory tow package was on it ?

In the bag with the pig tail for the plug under the dash for the brake controller, there is a relay for the trailer tow reversing circuit, is this installed ?
On my '01 it was in the bag, on my '06 it was installed already, all I had to add was the battery relay.

In the Tow forum, there is a sticky on the relay and fuse locations :

https://www.f150online.com/forums/sh...d.php?t=184757

I updated this with the directions for my '06 tow package instructions.
I scanned the full document into pdf format, if you want it, drop me an email in my profile. The bulk of the important pages ( linked in the thread above ) are in my 3rd album.

I am guessing without the reversing circuit being live, when the truck is in reverse, that checking the relay #301, and the fuse F10 ( 20 AMP ) is in order. If the trailer has parking lamps, I guess F10 is good.

If those are good, next step is to check that the normal reverse lamps work correctly ( no problem with the DTR sensor ) and that the coil on the trailer tow reversing relay is active ( good ground and power ), and the Circuit C238 is getting power.

The location of the Circuit C238 is in this thread :

https://www.f150online.com/forums/sh...d.php?t=233512

Good luck, let us know what you come up with on the questions.

Steve

 

I too am going to assume you've got the factory Class III Towing Package because if you do not, all you have is a flat 4 connector. You need the flat 5 to get the reverse circuit to lock (off) the brakes when backing up. The first thing I'd look for is a blown fuse on the trailer backup circuit. Like SSCULLY said, see if you're reverse / backup lights are working as your first clue. If you're in a real pinch and need to back the trailer up, run a temporary jumper wire from your running light circuit (brown wire) to the blue trailer plug wire. Turn your lights on and you'll be able to back up. I did that once for a guy at a launch ramp to get him out of a bind - no pun intended.

 

The problem was that there was a relay missing. I never got a package with it. The dealer installed it and all is fine. Thanks again.

 

There should have been the under dash pigtail in that package as well.
Did you have to purchase that with the brake controller ?