Silly fuel switch wiring issue.

[offalot]

I am just wrapping up a M-TDI swap in my 82 caddy. When I took the 1.6 idi out in the fall everything worked fine (well except for some alternator issues, still gotta get through those) I've got most everything wired up and only a couple wires left but am having trouble hooking up my fuel shut off switch on the IP.   Pretty much the only two wires remaining are Blue and blue/black. According to Bentley, it should be the blue/black one but it reads 0vdc with ignition on or off and does nothing when touched to the switch. The blue wire however reads 4.9vdc when on but when touched to the switch, makes my glow plug relay  (pimped ford starter solenoid) trip on and off. So I am kind of left without options. this seems like it is something obvious but I'm missing it.

[ORCoaster]

Got a shorted out wire there?  Run it down to see if cracked or broken in some place along the way. 

[offalot]

Would love to, but it enters the big ol' loom about 3" down from the end. I don't think this wire is fused and if so which fuse it is, to where I could check the resistance at the other end.  Not sure what could have happened in between taking the old motor out and this one in, but I suppose more could happen in that instance than just day to day driving.
I'm so close! this is frustrating.

[ORCoaster]

That wire supplies 12 vdc to the solenoid when the ignition is on does it not?  Can't you go to the back of the ignition switch with one probe and then to the engine side of the wire and at least test for continuity with the key and switch?  You should not have the battery connected for this test as you are looking for resistance. 

I know it is like the most difficult yoga move in the world to see the back side of the fuse box without at least pulling it loose first but I would think you would find that color combo someplace right there.