Trailer brakes locking when headlights on
 

Hello fellow ford people, Anybody ever come across a problem where trailer brakes lock up when headlights or parking lights are on, I have an 04 f250 SD any input would be greatly appreciated

https://cimg5.ibsrv.net/gimg/www.for...866009d994.jpg

Take a meter to the outputs of the plug on your bumper. Pin 2 and 3 are likely miswired, either on the truck or trailer side.

I agree, your 7 pin at the truck is most likely wired wrong.

Does everything else work?

Steve

Did this work correctly at any time in the past? (For YOU?)

Without more info there is no way to know if the problem is with the truck or the trailer as wiring can interface in either, if I am reading the OP's post correctly.

Steve

I bet his lights come on when he applies the brake. :)

If the problem is the truck, you can test the above hypothesis pretty easily. Apply the brake controller manually. If the headlights come on, the problem is the truck. If they don't, the problem has to be the circuit on the trailer as there is no problem without the trailer. :)

Steve

The OP hasn't been back on the site since the day he posted. I hope he finds his way back to us. :'( We could probably fix this one.

I wonder if he put the connectors together spun 180 degrees from correct. There should be a nub to prevent this, but if not, it would explain why when he turns on the lights, it activates the brakes.

I had the same thought. Unfortunately, we may never know...

You are correct..... this is day 6 without any feedback. BUT - he may be a once a week customer!

Hey guys I am having this issue with my 2014 F150 STX. I just had the controller flashed by dealer that I installed. The trailer brakes work fine and until yesterday I had never been out late to were I wanted to turn my head lights on. As soon as I did the brakes locked up. I was confused and unplugged trailer. Then when I got to my buddys I was telling him and he tells me the trailer is wired wrong. I pulled the plug and it looks correct. All the trailer lights work correctly, so could it be an issue behind the plug? I did follow the wires back from the plug to the battery box for the break away switch. There is a bunch of wires tapped into there but I haven't traced them out to see if they have the trailer brake wire tapped into a tail light wire by accident.

Welcome to FTE!

Question: did the truck *ever* tow with the lights 'On' (presumably headlights) and work normally with any trailer's brakes?

The first thing I check is the truck to make sure all the pins in the plug are good and getting voltage when appropriate. A simple multi-meter is good for this and a test-plug is a bonus.

If the truck checks-out as good, then focus on the trailer side by applying power one pin at a time with either a spare battery (including an inline fuse) or battery charger. By isolating one circuit at a time, it saves time by not ripping the whole wiring bundle apart.

Since the headlights don't really have a direct circuit to the trailer, it has to be the marker light circuit that is crossed to the trailer brakes, if that is the only circuit that activates the trailer brakes (I am assuming the trailer brakes work without a problem otherwise?)

I agree with what Jay is suggesting. First verify that the trailer brake pin on the seven pin on the truck goes hot when you turn on the maker lights. If it does, the problem is most likely the wiring in the seven pin on the truck itself, unless someone has messed with the wiring in the past. I posted a while back about one I worked on where the trailer brakes activated when the left turn signal was used, but that wiring was a real mess and the problem was obvious. :)

Steve