I am connecting a 7 way round connection for pulling a travel trailer. I am having a problem connecting the black 12v wire connection for charging the battery while driving. I was hoping to not have to run wire all the way to the front of the vehicle. I found that out of the main harness that runs to the back of the vehicle, there are two wires that come out and attach to the frame. A white and a black. I figure the white is ground, but does anyone know what the black one is?

 

If the black wire is attached to the frame just like the white wire is, then that would also make it a ground.

 

Old thread, but still helpful to towing hookups.

I just went through this yesterday. Factory 4-pin hooks up to the grey plug on the frame with the four wires. This supplies the lighting. The black plug with the black and red wires attached to the frame are for the brakes and charge voltage. Hope this helps anyone about to deal with this. On another note, those factory trailer pigtails are not easy to find anymore, so it gives you a place to start splicing a home-brew pigtail.

 

So I am having the same issue of no 12v to the 7 pin connector on 2019 F250 KR. I tested with the trailer plugged in and truck running. Pushed the break pedal and had the door closed. Best i got was 10.4v at the pin. I took it to the dealership under warranty and they confirmed it is not working. First test was the trailer control module (TCM) it showed on their test that it was bad. Mind you the truck only has 13k. They replaced the TCM and still not working. Tech Load tested the wiring and can force the TCM to produce 14.89v (same as the alternator). All the wiring is good, New TCM appears to be good but still wont work unless the tech uses the diagnostic computer to force the TCM to send the voltage. Field Service Tech could not figure out what was wrong so it was escalated to Ford Engineering Team. They are at a loss. Tech went through all the tests with me present and from TCM to plug (after being forced) all appears to be fine. My suggestion was the Body Control Module (BCM). I like the smart connection manager on truck when it works. They have pulled three brand new trucks with the same tow package and tested them and they are work. I guess the Gremlin crawled into mine and refuses to let go. Ford has had the truck almost two weeks now. Good thing is they have agreed to change my SYNC splash screen to to the Lincoln Black Label Splash (which matches the interior of the truck) for free. All warranty work but it has cost Ford a lot of money in Labor hours thus far. I hope they can solve the issue soon.