Last night I started the 'ol '93 and noticed the tach wasn't working and the amp gauge was only reading about a quarter of the way up (similar to when the grids are cycling, but the engine was still warm on this occasion and the wait-to-start light didn't come on.) The headlights were also dim. This was a constant drain, though--no cycling. After driving about two miles, the amp gauge shot up to where it normally runs (3/4 of the way up, 12-14?) and the headlights got bright and the tach started working. It was fine the rest of the way home.
I've noticed before when I'm driving that the tach will suddenly die, but it's been in the daytime so I didn't notice the dim lights, and never looked at the amp gauge. But now I think the tach not working is related to whatever else is going on??
So there you go. What do you think?

 

Maybe a sticky grid relay? It happened to me once.

 

Sounds like a flaky crank sensor. Check the gap and the wiring harness.