I donít know how much your charging system is like mine, but would assume the same. You could verify by seeing if you have metal 6v relay in your front run bay.
Before attacking the alternator do as Myron suggested to make sure you donít have a conflict of two sources trying to charge the batteries.
If all good, look at the alternator circuit. You have a fused ignition wire going to the alternator. That fuse must be good. Your front run bay is different than mine, I believe. Hopefully, that fuse is labeled.
Once the alternator is charging a 6v signal wire, that is attached to one of the three (doesnít matter which one) stator wires, powers the 6v relay. When the relay clicks on, it breaks the ground to the ALT FAIL dash light. So, if the alternator isnít charging, the light stays on.
This is the way the Leece-Neville alternator was originally wired. How and where they hook up that wire to the Delco alternator I donít know. Maybe someone else can jump in.
My white label on the relay
Just a better view of labels on original alternator