u/thekevo1297

Alright so a little back story 2013 ford 450 powerstroke. Before I started at this site our site manager removed the bed and had a flatbed welded to the frame and cut the rear wiring harness at the end of the flatbed. Fast forward to today and now I'm turning the flatbed into a service truck that needs to be road legal and installing new rear tail lights.

I've done wiring on semi trucks/trailers and garbage trucks but never ford pick up trucks and never completed a harness like this. So I apologize if I sound green here.

I've been struggling to get the reverse lights working and I'm not sure why. I called the dealer to get schematics and wiring them according to the diagram (which I may be misreading) has not been working.

Running the blue wire with the white trace to the reverse lights and lights ground to the black/white ground I've gotten no voltage to the lights in reverse. When I run the gray and brown wire to the lights and the black and white ground I get voltage but always when I press the brake pedal not in reverse which is no bueno.

Would anyone have any insight as to what I'm doing wrong? Or if it's an internal wiring issue I should be looking for? I checked the fuse and it's still good. I would love to feel stupid here honestly because I could learn some thing from it.

Does anyone know why the harness splits in the back? My guess is trailer lights? The smaller split side also has a separate gray/brown, blue and white and black and white ground.

Also one of these wires (I am home now and cannot remember which one) consistently gets weak pulsed (on/off/on/off) voltage of about 2-5 volts in reverse and I have no idea why.

I know wiring stuff is a lot easier in person and I don't expect any miracles here but Id rather ask and finish this project sooner rather than struggle and make it take longer. Appreciate the help.