There are one and two wire GM alternators. I can't remember the scoop on them. I think your white wire goes to ignition hot with key on but don't hook it up till I talk to a friend of mine. If I remember right some alt need to be turned on or excited by the signal from the switch. Some are one wire and self exciting. Take a screw driver and dangle it between your fingers with the tip almost touching the rear bearing cap. It the alternator is charging just above idle and higher the screwdriver will magnetically stick to the bearing cap. You should be putting out 14.0+ when everything is working. Always start at the battery but I'm willing to bet it's the way it's wired.
I'll call my friend tomorrow. He knows a lot about the GM alternator.
Liz, covid, murdered 10/19/21