So, got some things done and rewired (radiator cooling system).
Turned the key to accessoy to verify switches, and noticed my trans temp gauge hit 180, and slowly climbed to 195. The pan doesn't even have fluid in it :laughing:
Turned it off then back on, same thing.
Looking around, looks like something isn't grounding properly.
Thinking about it, I used Permatex high temp sealant (it even states to use sealant in the Autometer instructions.
Between that, and the pan using sealant between it and the transmission, I don't think the pan is well grounded. There's the dipstick tube, but that was painted and the engine there wasn't really a good ground.
So looks like I might need to add an additional ground wire between the bung and the hex head of the sender, as the sender grounds through it's threads.
Pan fluid looked fine, and didn't smell burnt...so I'm pretty confident I've just got a wonky gauge/ground situation.