This is a frustrating issue. I was having the same problem. Replaced the 7 pin cord and connection box on the trailer side. Pulled the harness from the back of the truck's 7 pin connector and cleaned everything thoroughly. When it was all said and done, the solution was to replace the trailer's LED tail/brake/blinker bulbs with standards. Problem solved. It is shocking to me that a truck that is 100% LED lighting can't deal with having LED lights on a trailer.

 

Yes. I was very surprised when Ford service headquarters on support said they were aware of the issue and fix was fix it yourself. I fail to see why it is an issue to start with since they are aware of the less current drain and many trailers now (like trucks) have LED's instead of conventional bulbs. Looks like a programming fix would take care of... Or maybe instead of making all the trailer stuff work without this working. For years everything on the trailer side has been protected through relays not to interfere with the truck electrical system. Why do we need some special resistance check to cut on/off. I am not electrical engineer but looks like they over build that part. Anyway, for being the leader in trucks, they get a big "F" on this to me... Just my opinion,,,,,

 

 

If you are referring to my trailer, yes all the lights are LED from the factory. Another interesting thing before I ordered the F-450, I had a 2017 F-250. Pretty much same setup only pulling a 14' enclosed cargo trailer with LED lights. Never had any issues with the F-250 and error trailer not connected.. It did have electric brakes where as the DRV has electric over hydraulic. I first though maybe the electric over hydraulic was the issue. But since you configure in the panel for those instead of electric brakes figured it would know. Another though I had was maybe since the LED's are seven(per housing) I think instead of some having many more LED's. My trailer has 3 of the 7 FED lights on each side... Anyway, at this point it seems like the Curt adapter is going to work for now. We are planning a trip middle of next month for a short 400 mile trip to check out the F-450 in pulling the DRV. It will be quiet different than pulling with the International Workstar.

 

So I connected my truck and trailer using my jumper cables. No change. Cleaned the male & female connection at the bumper. Nothing.

Crawled under there and looked. There was only 1 of the 4 wheels that had both white wires connected to the wheel!

So that's probably my issue. Still waiting for my brother to come over to connect and see what issue he may or may not have.

But I'm a little confused. Each wheel has 2 white wires connected to the wheel. I can see one breaking off. But wouldn't it have thrown a fault as soon as the first wire came off? Why is it waiting until now, with only one wheel left connected, to throw the fault?

I guess it could be that if it had at least one brake connected on each side, it had a complete circuit to at least one brake (even if the are two wheels on each side) on one side. I mean, the truck doesn't know ther trailer configuration. 2 wheels, 4 wheels, brakes on all 4 wheels, whatever. It just knows there's a trailer back there with a brake on each side. So as soon as the one side lost all connectivity, that's when it threw the fault.

And my other guess is that's why we've been gradually ratcheting up the brake gain. As each wire broke off, we had one less brake slowing down the trailer. I'll bet when I get all the wires connected, it would leave a black streak on the pavement 20 yards long if i leave the gain at 9.5. LOL.

Does that sound like I've got a handle on it?

 

Yes, that is going to be a big part of the issue since you have eliminated other causes. Hook up the wires, confirm with a buzz at each wheel when you pull the slider on the TBC. A buzz means the brakes at each wheel (magnet at least) is getting power.