I have an '08 F350 6.4l, It came with a shell on the back that is an A.R.E. brand, It's a very nice shell but the lights don't work, either third brake or internal dome light. It has a standard 3 wire plug


and I traced the wires and found they weren't connected to anything anymore. My question is what goes where?
I have included pictures of what I think is relevant. The black wire is split to both brake light and dome light the red goes to the brake light. The white goes to the dome light.




After the plug, the red ties into a green/yellow wire right by the spare under the bed


and the white and black go about 5 feet up the frame then are just bare. This is really simple and I should know to fix it but I have been working pretty crazy hours and can't think straight but need it up and going for a weekend camping trip. So can someone do my thinking for me lol

Any help or suggestions would be more than appreciated. I'm glad I found this forum and hope to contribute more in the future.

 

Ground the black wire and the third brake light should function normally. Run a fused wire from the battery and connect it to the white wire for the dome light.

 

Thanks a million, super simple

 

What size wire would you recommend to come off of my battery and to the white wire with?

 

14ga will be just fine

 

On my 1997 F150 I did not run a separate power wire back for the cap dome light.
To do this, the brake wiring stays like you have it in the diagram (but connected), and you use it to charge a small battery that powers the dome light.
I tee'd off the green CHMSL brake wire and ran it through a diode to the hot side of a small sealed 12V battery out of an uninterruptible power supply (UPS). Wire the dome light to the battery and it doesn't matter if you forget and leave the light on all night, it won't run down the main vehicle battery.
Each time you step on the brake the little battery gets some charge.

And the diode keeps the battery from back feeding the brake light circuit so the brake light on the cap doesn't stay on all the time
This worked great, I used it for a couple of years on the same UPS battery. I even left it on all night on purpose just to see how long it would run and it was still shining just as bright in the morning.
This is also a handy way to get a 12V power source at the back of the truck to run low draw stuff like a phone or laptop charger. Just be sure to put inline fuses on everything.
FYI, anyone else looking to add a cap, at the factory Ford leaves the green brake wire hanging out of the harness at the back of the truck.

 

Make sure you put an inline fuse in there for the dome light.