Electrical gremlin. Dart won't start. Desperately seeking insight!

EDIT: this is a '72 dart 4-door

Okay, so this gremlin has popped up in the past, but never this persistently.

When it first happened, the can just wouldn't crank. So I popped the hood, jiggled some wires, and that was that. Started right up.

Then the car shut off a few times while driving down the road. No biggie, I pulled over, popped the hood, jiggled some wires and... it wouldn't start. Hmm. New fix: Open door, slam door shut, and bam! Started right up.

That was it for a couple months. If it stopped running, or just wouldn't start, I'd open the door or hood, close it hard, and it'd be fine. Still thinking it was just a loose wire somewhere, it wasn't a major concern.

Then it happened about a week ago. None of the above worked so in a last ditch effort, I moved the shifter from park, all the way to 1st and back to park. Tada! Started right up.

Now I've got a problem though. Nothing seems to be working. Er, at least none of my previous "remedies" are working. When I open the doors, the dome light turns on, and I have 12.58V at the battery. Yet, nothing happens when I turn the key. No click, no starter, no vroom to speak of.

I haven't had time to really get under the hood and troubleshoot yet but I'm guessing voltage regulator, a relay, or a fusible link? I dunno.

So my question to y'all is weather any of you have had this sort of issue and what your guesses are.

I won't be able to roll my sleeves up until Thursday and getting to work is a bit of a PITA now.

A million thanks to any and all who may share some wisdom (or even just guesses)

~Rev