I know all of you must have been holding your breath waiting for an update, so I am here to say, relax and breathe.
The connections at the firewall were corroded to the degree where some continuity was able to pass through but enough to prevent a solid connection. After a thorough cleaning of that connection, plus cleaning the wires at their far ends, (horn relay and starter), the gauge is working as designed.
As for the needle being pinned: I kept applying a AA battery to the gauge terminals repeatedly for about 20 minutes until the needle bounced into the zero position. With each application of the 1.5 vdc to the gauge, the needle eventually got closer and closer to zero until it remained where it should be.
I was dreading the thought of removing the gauge. That's why I am happier than a pig in chit.
Okay, fellas! As you were.
