Alternator gauge is smoking
IMHO if the alt gauge is smoking you need to pull the gauge out and have a good look at it
I recently purchased 2 67 - 69 dart clusters, I was looking for good temp fuel gauges. BOTH had trashed alt gauges. One the posts were completely loose in the gauge, so it would create a high resistance under load and got hot enough to melt the pot metal housing.
The other had the posts twisted to the point the metal it is attached to was touching other metal parts. That would have made a direct short.
I can provide photos if need be