Odd electrical gremlin. no start, dim dome light (some times) buzzer comes on and off

'72 Dart Custom Sedan.

Alright, this one is baffling me and I'm not sure where to start looking.

Last Monday, I parked my car after coming home from school. I've had no issues that lead up to this.

Tuesday morning, I go out to my car and it wouldn't start.

The dome light was on, and the buzzer came on when I put the key in, but I just got a "click", then the buzzer stopped, and the dome light dimmed.

I've gone out a few times to try to figure something out but there doesn't seem to be any method to the madness.

Just now, I went out to work on it. Initially, the buzzer wouldn't come on and the dome light was dim. I checked the bulkhead connectors, wiggled the connections at the relay, checked the battery terminals etc. Still nothing.

I crawl under the dash and double-check the fuses. None are blown. But as I'm down there just staring at the fuse panel (not even touching anything), the key buzzer comes on and the dome light pops back to regular brightness.

Hoping that I'd stared the gremlin into submission, I turn the key. Just got a click, the buzzer stopped, the light dimmed, and I'm back at square one...

The battery is good. 12.44V

At first, I thought maybe it was the ignition switch, but I don't see why that would effect the dome light when the key isn't even in.

I cleaned up the bulkhead connectors about a year back and gave them some anti-corrosion stuff so I don't think that's the problem.

All the fuses are good, but I don't know if there are any fusible links elsewhere.

Anybody ever have similar issues? I don't even know where to start looking. It's like the entire system just crapped out.