I'm about at my wits' end here. I'm willing to take suggestions or the name of a reputable, solid shop between Louisville and Nashville at this point.

* I've checked the two panel wiring connectors. They are good. I've got dash lights, turn signals, the hi-beam light.
* I have the key-in buzzer. I do not have the seat belt buzzer. Both are known good.
* I do not have the BRAKE light or the FASTEN BELTS light. Both have worked in the past.
* I do not have the TEMP gauge. This usually doesn't work, but it bench-tests just fine.
* I do not have the OIL PRESSURE gauge. Bench tests fine. Usually doesn't work.
* I do not have a FUEL gauge. I loosened and messed with the ground for both fuel gauge and fuel pump. Nothing, except the pump output changing based on ground quality.
* I have lights, wipers, turn signals, hazards.
* I have moved the dash ground wire around to four different locations, all of which should be suitable. Nothing.
* I have an RT-ENG voltage regulator. No LED light. I've changed in a different volt reg, not sure if functioning, but didn't improve the situation. Will pick one up from the local parts store to test.

...what the hell else could it be?!?