About 2 months ago, I noticed that with any trailer I plug in there were no power to trailer running lights. With a new heavy duty bumper, the original 7pin and 4 pin factory installed plug will not work so I am changing to a new hard wired plug. In checking all wiring in the factory harness, the brown wire which is for running lights has no power. All others are fine.
I do not have a wiring diagram to see if the wire is spliced somewhere in the harness to connect the truck tail lights which work fine. Those wires are to small to carry a trailer marker light load so I though they may have spliced along the harness near the rear of the truck.
Does the brown wire go all the way to ??? and is it fused???
Need some help finding the issue.

2018 Ford F250 Super Duty

Thanks
Vic

 

There is a fuse for trailer tow lights in the power distribution box under the hood (30a as I recall)
check your manual for location.
I just did this on a friends 19

ZooDad

 

Fuse 99 on the 2018, I had almost the same problem. The fuse had continuity across it but I was only getting 3.7 volts. Replaced the fuse and all was good. If you are .looking at it from the passenger fender/front, it's the very back right fuse closest to the motor. 30 amp.

Did you unplug or plug in the 7 pin while the truck was running? If so, there's your culprit.

 

Well that was it! Fuse 99.
I must have unplugged while running many time but I guess the truck objected.
Thanks for the help!!
Vic