My amp gauge on my 14,000 '72 Pantera started pegging out at +75 amps. Bought a new one from Mike Drew. Upon pulling the dash to remove the old gauge, I see that the amp gauge (both old and new) have two terminals marked "+" and "-". But, on my car, the gauge in there now (which was working when I first bought the car) has a black wire hooked to the "+" and a red wire to the "-", which seems counterintuitive. Is this correct?

I believe those connections are correct but if the gauge is pegging I would look for a problem somewhere in the electrical system. Does it peg to the plus or minus side?

"+" side.

When my amp gauge pegged positive, it turned out to be a loose connection at the back of the gauge and it ultimately burned out the gauge and (not certain if it is related), but my voltage regulator also blew which in turn boiled the battery, I've since replaced the VR, and then the ammeter with a volt meter (I haven't seen it lately, but there's often a guy in Cyprus selling Veglia volt meters on e-bay, not an exact match, but certainly safer).
My travails: "No Smoke - Yet"
There's lots of good stuff about the ammeter on PanteraPlace Pantera Ammeter ... pay particular attention to the part where it shows the right combination of lock washers, washers and nuts to ensure a solid connection.
Hope this helps.