Ground was on body-colored metal, right about where the (aluminum?) under-dash cross bar slides into, close to the fender.

Latest update: attached fuel sender and had a fuel gauge for about five minutes. Started to notice the temperature gauge going for the moon, cut power. Exchanged out the RTE limiter for the original one, managed to yank out the negative wire for the fuel gauge in the process from the dash. Reattached that connector to it's pin, now I have no fuel gauge, no seat belt buzzer, a temperature gauge hell-bent on hara-kiri, and for that dash of salt in the wound, a dead battery.

*sigh* Guess this cluster is coming back out...

(after calming down) Ok, something is wrong with a gauge. The RTE limiter has a diagnostic LED. If it flashes when power is on, everything is happy. If it cuts out, like it did last night, that's a protection measure. Today, that LED is solid on, indicating a short to ground. Just off of the cuff, I'm going to ring out the full temperature gauge length, from sensor to gauge. I still want to pull the cluster and properly sort out the fuel gauge's negative wire issue. The fuel gauge coming to life gives me hope.

(after a good night's sleep) Noticed that a 12v battery wouldn't start the car and would discharge fast, even with a jump box attached. Pulled temperature gauge, no effect. Found that fuse #6 (5 amp) is blown.