Alternator gauge is smoking
I don't see anything obvious at the gauge itself. Mattox brings up some good points. "Something" causing excessive current in that circuit, either a load/ short, or very high charging current AND OR a loose connection
This is, really all the fuss about upgrading, rebuilding, or eliminating the ammeter circuit. The main trouble areas are...........ANY terminal in the circuit, from out in the engine bay, through the firewall, at the ammeter, and back again, or looseness at the ammeter terminals.
One thing you might do is to rig it up (you don't need the cluster) and bolt the ammeter wires together, tape them up temporarily, run the car, check charging voltage and LOOK for hot wires, all the way from the fuse link, through the bulkhead, include the two ammeter terminals, and back out on the "big black," back out the firewall to the battery
I WOULD ALSO check the "welded splice." Go to the black ammeter wire terminal. Unwrap enough of the harness (a few inches) and follow the big black down the harness, until you get to a big splice. Unwrap and inspect that splice. They are welded but THEY HAVE AND DO fail occasionally.