UPDATE:
Well, I finally got a new multimeter and some time today to troubleshoot the problem.
First, I had juice at the voltage regulator fuse. Good.
Then, I had juice at the switch/breaker. Good.
Still had NO indicator light on the Zefftronics voltage regulator. WTF? It was clearly getting electricity.
So, I took the voltage regulator off the firewall, visually inspected it and reinstalled it. Bingo -- I get a green indicator light on the unit.
Bad ground? Must be. Maybe a little corrosion under the grounding wire? Who knows?
So, after consultation with my friend Tom Berge, I've run a secondary ground strap from the attachment bolt (that I had ground the VR to) directly to the grounding block mounting bolt that has the grounding strap going straight to the battery.
It just don't GET any more grounded.
Sadly, I didn't have time to test run it, but the green LED on the VR itself is a good sign, and I'm pretty sure that the problem is licked. We'll see how she runs tomorrow.
Thanks, everyone, for your help!