Gauge power is in to the post with the reg tag.
PROGRESS! I completely disconnected the ignition switch and the gauge problem disappeared.
I suspect one of the wires was miswired at the ign sw- I had to re-connect it during a dark rainstorm a few weeks back.
Or the switch is bad.
Anyway, I have another switch and will connect that one up.
I think I have it figured out - as long as I can get the leads connected to the correct ign sw posts!

Thanks!