Hi Tim,

The ignition switch to starter solenoid is a straightforward wire, no more complicated than the one you made up to start if from under the hood. The blue wire that connects from terminal 50 on your ignition switch socket runs down to a connector under the carpet just to the left and a little forward of your M47's shifter, where a jumper plug substitutes for the lack of a neutral safety switch.

From that plug, at the same terminal, a blue test wire runs back out under the hood to a test socket (for cranking from under the hood) you'll find just above the valve cover on the firewall. The other side of the jumper plug leaves in blue/yellow to go directly to the gray 8-way harness plug on the firewall, and then through the suspect engine harness directly to the #50 spade lug on the starter solenoid.

Yes, I agree, it sounds as though a crimped spade lug has become loose and corroded, and I would look outdoors first. Post back if my descriptions of where things are don't seem to make sense. If you can make it run by your coax jumper (or a screwdriver from terminal to solenoid stud) you won't need to worry about ignition system or fuel system computers.

PS - If you get a moment can you explain the movement that makes your speedo needle pulse like it is in water? Sorry, not following. Don't get the connection to the transmission seal either.
--
Art Benstein near Baltimore

What's the definition of a will? It's a dead giveaway.