Thanks for the details, here is the most likely suspect
First, a bit about "how these work". The isolated field alternator brings the field connections out to the two terminals. They are electrically interchangeable. When you turn the key to "run" the switch sends 12V to one field terminal, and to the VR, WHICH MUST BE GROUNDED
The VR sort of "controls the ground" on the green wire which hooks to the remaining field
Since you disconnected the green field wire, this means that field terminal is grounded, and SHOULD NOT BE.
You need to remove the alternator and inspect the brushes/ brush holders for improper assembly, breakage, or missing insulators.
THIS IS A COMMON problem, as these alternators are commonly sold as replacements for the older 69/ earlier vehicles which HAD only one field, and so some of them come boxed with one of the two fields grounded. Also some of them come improperly assembled
CAVEAT. You lucked out!!! If you had accidently connected the blue field wire to where the green is, you may have burned up some wiring, as THAT CIRCUIT IS NOT fused.
