On the cab side of plug, opposite brown/pink wire is 2 wires together as you've been saying (only I wasn't getting it). There is a solid red (slightly thicker), and brown/light stripe (appears white or light tan, but possibly faded pink). NOW, here's what I'm getting on those two wires separately; the brown/white I'm getting zero volts on run position, and full 12v on start position. Yay. On red wire nothing on run, nothing on crank. I was expecting 12v only on run...and assumed that would be the wire that would get the resistor wire. But nada. Is that fused?
Yes, on the "red wire", after it has been cut from the Brn/Pnk wire (at the C102 terminal), you should be seeing +12v with the ignition switch in "run". There's no separate fuse just for this wire; all of the ignition and start circuits from the ignition switch share a common fusible link (E).
"if it were me", I'd try to troubleshoot and correct why the Red/L Grn is not having power in "run". Two things I would check:
1) On the round black plug with two wires, does the Wht/L Blu hashes show +12v in "run"? Notice on the wiring diagram this wire and the Red/L Grn wire are both tied together at the ignition switch. The black round two wire connector is C107.
2) Test the Red/L Grn at the ignition switch itself. Two Phillips screws from underneath lets you pull the plastic cover pieces When you do this, look closely at the ignition switch- the electrical part a little lower on the steering column, not where the key goes. See if there's a gap between the metal and plastic parts, and give the wiring connector a wiggle to see if there's any looseness between the two pieces. It's not uncommon for these old ignition switches to get loose and cause problems; look for a gap like this:
If your ignition switch is loose, you can put a tie wrap around it (like in the pic) or replace it. If your Wht/L Blu is good but the Red/L Grn isn't good, that could be an alternative, but my own preference if it were my truck, would be to find and correct whatever is wrong with the original Red/L Grn ignition circuit.