Alternator wiring issue

[mopar jack]

To verify that the alternator is good I would disconnect the 2 field wires at the alt. Next run a jumper wire from the battery + to the field position where the blue wire goes then run a jumper wire from the field location that the green wire is connected to and temporarily connect to ground. You should have plenty of voltage out of the alternator.
Your problem seems to have started when replacing the valve cover. The cable bundle that runs along the valve cover gets very brittle from the heat and oil vapors over time so that's where I would start looking for broken wires.

[Luca]

Ok I think I got it. Found this wiring diagram. The second field terminal has to go the side of the ballast resistor opposite the terminal that come from the coil+. This energizes the field and now charges the battery

[YellowThumper]

Alternator needs a place to charge to. If the main wire has burned out fusable link, it cannot push a charge.
Confirm you have power still feeding the field wire.
If AMP guage is still in use I would also check to make sure the firewall bulked connection is not burned thru.