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nguyenbio's avatar
nguyenbio
Explorer
Aug 02, 2017

F350 Trailer wiring fault when towing my XLR

Okay here it goes. I have a 2015 F350 towing a 2016 XLR. For over a year, everything was fine. About two months ago, I slowly started getting a "Trailer wiring fault" message when starting off a trip and then sporadically getting "trailer disconnected" and "trailer connected going on and off, even though the trailer is connected the entire time. During this time, all my lights work and brakes work perfectly.

Lately, when I take off at the beginning of my trip, the wiring fault message loose us after a few seconds at idle speeds, all lights work but no brakes. After a few seconds longer my brakes begin to work. During my driving at highway speeds I always check my brakes when the message sporadically pops up and have never lost my brakes at highways speeds. When I get to my destination and slow down, the wiring fault pops up again, I loose my brakes again at idle speeds.

I have checked and used both the bed receptacle and bumper receptacle and the same symptoms exist. I tried to go underneath and wiggle the trailer brake wires and cannot replicate the problem. I've cleaned and use dielectric grease on all connections and same results. I also double checked the j box to ensure all connections are tight. No connections had water intrusion

My next item is to test each magnet and re-run all axle brake wires to the outside of the axle. This is the result of talking to Dexter. I may redo all the brake wires period!

According to Ford, the problem is only on the trailer side if the wiring fault pops up when no trailer is connected. I guess one bad magnet will send the trailer fault message to the integrated brake controller and the truck senses that all brakes are bad. Dexter and Ford agrees it's usually the trailer and not the IBC.


Does anyone have any ideas or experience with this?? I would tow another trailer or have another person tow mine but I don't have any friends with fifth wheela!

15 Replies

  • lincster wrote:
    Yep, has happened to me a couple of times.
    If you spend enough time, you will find the broken wire or bad connection. it is there somewhere in your brakes on your trailer.
    Nothing wrong with the truck or the plugs in the truck.
    100% somewhere in the trailer.

    This is my experience with this exact problem. Ended up being a worn drum brake magnet and associated wiring.
  • I had a bad Integrated Trailer Brake Controller (TBC) on my 2005 F350 that was giving me a similar problems. I would try another trailer first before i started digging into the wiring... if you have access to a bumper pull trailer with electric brakes, it might help you troubleshoot a bad Trailer Brake Controller (TBC) too.
  • I know this might not be your problem, but if you haven't checked it out its worth a look. With one of our many trailers, the factory attached plug was the problem. As soon as we hit a big bump or turn just right, the truck would say trailer disconnected. It would happen so fast that the lights would just flicker for a second. We buy one like this and have used it on multiple trailers. https://www.etrailer.com/Wiring/Hopkins/HM48510.html

    I hope you can trace the wires if that is your problem. I can't trace mine very far. Good luck.
  • Crawl under and take the time to remove all the feces connectors on the brake wiring if you can get to them, and either solder / heat shrink all of them or replace with Scotchlok IDC's. Soldering is better.
  • Yep, has happened to me a couple of times.
    If you spend enough time, you will find the broken wire or bad connection. it is there somewhere in your brakes on your trailer.
    Nothing wrong with the truck or the plugs in the truck.
    100% somewhere in the trailer.