Ok some of you are gonna think I'm crazy here and I'm starting to think the same thing. PO installed 4 aftermarket fog lights in the front bumper. They are too bright for me to use so I figured I'd take out two and put them on the rear and wire them to my reverse lights. They have worked flawlessly since I got the truck. Pulled out the two I wanted to remove and just cut the wires where they were tied into the original harness. Tape everything back up and now the two I didn't mess with don't work. Do some testing and the circuit is dead at the lights. Found a connector in the harness below the battery and no power there either. Had to go all the way back to the switch to get power. So I add a jumper wire to bypass the original and got everything connected and lights work fine.
Here is where it gets interesting...with the key off, the lights come on and off as they normally do. When I pull the switch for the fog lights, the console lights up, glow plugs come on and injector buzz starts. Exactly as if I had turned the key on but I haven't. Truck will starts fine. Also,KOER if I turn on the fog lights, they will not go out unless I turn the truck off.
I didn't mess with any circuit but the fog lights and how in the hell is that making the ignition come on? Any clues or suggestions are greatly appreciated as I am almost afraid to drive it for the fear of frying something.

 

It would seem your bypass wire is going to the wrong place?
Reverse everything you did, and start over.

 

I agree you with marksman. What blows my mind is how did the ignition circuit get involved. I tapped into the fog light wire coming out of the headlamp switch and tied it back into the fog light harness just before the lights. Even if I had botched that royally, I don't understand how the ignition became involved.

 

Yeah I'm at a loss here. Based on the attached diagram, I tied a jumper wire into terminal 5 and ran it to the fog lights. Fog lights worked but the ignition came on. Once I took that wire off terminal 5 the ignition no longer comes on with the fog light switch nor do the fog lights. If I run power (coming off terminal 8) straight to my jumper wire my fog lights work fine. If I splice my jumper wire back into terminal 5 and put power to it, fog lights and ignition come on. I have no idea what's going on in there except maybe a short in a wire somewhere. With my lack of experience and knowledge with wiring and schematics I would probably never find. Guess I will just run a separate circuit and switch for my fog lights. Just really aggravating as there was no issues with any of it until I took two lights out of the circuit.

 

Honestly, if you don't know what the PO did, you might just want to start over. Rewire the lights yourself to a switch, rewire the switch, and you'll know exactly what it's doing. Who knows what they wanted or did, and tracing it or troubleshooting it will take longer in most cases than just rewiring.