Used truck cap wiring in brake and interior lights
 

I just bought a used Eagle truck cap for my '05 Super Duty (8 ft.). The current wiring on the cap is a flat 4 trailer harness that connects to the cap's 3rd brake light and the interior light. If I get another flat 4 and use the mating half, where do I tie into for power? I don't want it to look like a cobbled mess. Any help on nice wiring tips is greatly appreciated. My truck has the factory trailer wiring.

Thanks,

Just tie the mating end of the new pigtail to the factory trailer harness under the bumper. Use scotchlock connectors and mate the green to green, yellow to yellow, etc. There should be a hole inside the bed in the corner stake pocket. If not, make one and route new wire harness from under the bed and through the hole. Zip tie any excess and tape the scotchlocks for a neat finish. If your cap does not have running lights (only interior courtesy), then use the brown wire in the harness. Tie it into a 12V+ switched wire. Find this with a tester at the factory trailer harness. CAUTION-If you fo this, make sure to never use the 4 way plug for your cap as a trailer plug!!. If you really want to do it correct, ground the white wire on your harness to the frame. I've found this solves alot of problems down the road.

re:
 

I was wondering if there was an adapter that plugged into the OEM harness? When I had my '95 F150 I bought an adapter, actually two differt adapters. One had a flat four and the other a 7 pin. On the other end was an OEM type connector with a male and female connector. All you did was separate the OEM connection and plug the adapter in between. I'm thinking if I had something similar it would make a much cleaner appearance. I had mail ordered those adapters back in '96 before I has internet and forget where I go them?

Thanks,

As a general rule, cap installers will tap into your back running lights for lights in the cap.
If you so desire, you can run a hot line up to the battery with a fuse in line for bed light without requiring parking lights to be on. You can also run it to your fuse box if you want switched power. If you want to hook into the trailer circuit, you can buy the harness at any boat store and most auto supply stores.

Got any Pics? Of that setup I have an 05 CC as well

yes go ahead and use those efffffing scotchlocks if you want to have nothing but grief with electrical gremlins down the road. those things do not belong in ANY quality wiring job, they get loose, corrode and generally fall apart, just not good for automotive apps involving moisture. particularily if you want it to last for a long time

Re:
 

I picked up somewhere on the web last night that Ford has a green wire in the rear harness for tapping into a 3rd brake light? I didn't get to look yet but will tonight. Anyone know about this wire? If that wire exists I guess I could tap into that for the 3rd brake light, ground off to the frame and off the parking lamp wire I could tap into for my cap interior light. I figure if i go into the parkign lights there will be no accidental leaving the interior light on?

Ceck out this thread https://www.ford-trucks.com/forums/7...ight-wire.html.

My 08 had the green wire sticking out of wire harness behind the hitch. The wire had marking tape on it. Tape was marked HMSL (high mount stop light).