sorry but you'll have to follow the wire from the 50 amp fuse to see where it goes....
I 'assume' that the splice is made where the wire 'T's off to the ignition switch ?
If the harness is taped ( usual...) you just carefully cut the tape ,peel back a few inches, locate the fat red wire and see what they've done.
Have you any access to the back of the fuse box ? See if there's any corrosion where the fat red goes to the 20 amp fuse ?
the '.34 volts' sounds like a well rotted out wire to me... just enough strands left to pass a small voltage.
I suspect the fuse block area and not a 'tap' in the wiring harness....
Ok so.
TODAY we had 12v at the 20 Amp AND at the solenoids r/w. (Major head scratcher).
At some point I look at the fuse box and the contacts slot for the 20A. One side seems a bit stretched too wide to make good contact. I grab a flathead and bend it back in. So maybe this was causing the incremental no voltages.
So, try and start? Same issue. I'm getting near my surrender point.
So after the solenoid we have the OPC and meter panel. The (broken) wire for the meter panel now shows 12v. That's a first. So now we're in business.
But the OPC still isn't showing 12v at pin 6. I jiggle, push, and test with a copper wire a handful of times. Nothing. I'm suspecting the plug, but it just seems too solid.
I give in and start untaping the harness. Pain in the butt. I Finally. Finally find the splice and the ultra small pin 6 wire.
It slides right out with a tug. I strip the wire, get 12v on it, and we're cranking away.
Mystery solved.
I owe you a beer for your patience and help, so feel free to message me a payment method