Voltmeter had been dipping randomly on the road for a couple hundred miles before this happened. Whenever I checked the voltage at the battery, it was 14.5v while running so I didn't think much of it. Recently completed a 200 mile drive with the car, parked it and let it sit for two months. Took the car out for a 5 minute drive to fill the tank (all gauges were working), drove it back home and parked it. The last drive was a totally normal, quick drive that didn't even heat it up all the way. The next morning it wouldn't start, I lost gauges while cranking, may have been a fizzle noise but I could be misremembering, and I haven't gotten it started since. Car has a history of getting wet sitting around outside not being used much, and the first start was always a 10-15 second crank. It's now garaged and totally dry.

Brief specs:
-89 IROC-Z 5.7 TPI
-VATS deleted via bypass at the relay and square wave generator wired into the ecm.
-Negative battery cable is 3 years old, both ground connections were cleaned today, no change.
-Cleaned ground strap from engine to firewall again. It didn't look very bad, assuming grounds behind the head are in similar condition and I have also cleaned them before.
-Cleaned ground connection underneath steering column. Again, wasn't that bad, has been cleaned before.

I can hear the fuel pump prime, I get power windows, HVAC fan turns on, I have all my exterior lights and they are appropriately bright. Blinkers are very very slow. Engine turns over fine but I have a VATS delete so there's nothing stopping that circuit anymore. I can see the blue light on the square wave generator blinking so it has power as well. No power to the coil. Coil tests ok.

I twisted around the fusebox and briefly got the gauges to move and warning lights to light up, but I can't keep it connected for any period of time and it's been a while since that did anything at all.

No blown fuses. I also checked the one behind the battery. Fusible links down at the starter don't look burned, old but the same as they have always been.

Any ideas of where to start poking around? It does seem like a ground that just got really bad but I have no idea where it would be and I have cleaned all the ones I have found either today or at some point in the past 3 years.

UPDATE: I started reading the FSM and probing around for power. Got 12.12v on GAGES fuse. Reinserted the fuse, twisted it around a little, and the tach reset. I get voltmeter, temp gauge goes straight up when cranking. Fasten belts light is working with chime, I got the SES light to come on and Security light comes on / goes off as expected. Jumpered AB at the ALDL port, got repeating code 12 and fan came on.

Still doesn't want to dial to life, but less mysteries.

 

"I twisted around the fusebox and briefly got the gauges to move and warning lights to light up, but I can't keep it connected for any period of time and it's been a while since that did anything at all."

Hi Komet, This statement right here indicates you have bad connections in the vicinity of the fusebox area, I'd be (disconnecting the battery and) taking apart the connections in that area and checking for burned contacts in the connectors. The bad connection(s) could be anywhere in the area from the fusebox to the wiring harnesses in the area, even as far as the ignition switch or the C100 connector. Your biggest tipoff is that you state the ignition coil ain't getting power, chasing that circuit from the ignition switch towards the pink wire at the coil is sure to turn up the reason why power has been lost (and is partially restored by twisting things around near the fusebox)

 

So all the dash issues were solved by the flaky gages connection, and I also confirmed I was having a no spark issue with a spark checker.

Went through the no start flowchart in the factory service manual and ended up at "Basic HEI Issue". Could be ICM, could be distributor itself. My distributor was super corroded and the ICM was the wrong one that retards timing, so I replaced the entire distributor with a new one from Speedmaster. My coil tested ok but I replaced it with a new AC Delco one as well since it was also rusty and old. She fired right back up with the new gear.

Ended up just being a couple issues that happened to coincide.