Alternator wiring issues

pt70 said
the large red wire on the alternator output appears to go to a ground on the fender. If so, this is wrong. It should be a #10 black wire going into the center section of the bulkhead connector. Then go to the ammeter, out the other ammeter terminal, back thru the bulkhead connector, then to the starter relay on the left fender. Do all wiring work with the battery negative terminal disconnected. Before reconnecting the battery, close the doors and test the current draw with a test light.

It sure looks like that in photo!
Could be an insulated stud, from which it could have one wire to the ammeter and a seperate wire to the main splice. Hard to know without seeing more.

7duce swinger said
It is the square back two fields

All that "two field" means is that it has two insulated field terminals instead of one grounded terminal.
In the photo we see a wire from each leading back to the firewall. So it should have the voltage regulator with the triangular connector. (#5) in Dana's list.

Dave above says the light purple in the back goes to the temperature sender. So maybe that's it.
Get '72 Service manual. That will be the most accurate way to ID any color & wire size and position in the bulkhead other than an expert familiar with that year.
Some colors and sizes stayed the same for many years, but not all.