[VetteVet]

If you ran the red wire from the firewall junction block all the way to the positive battery terminal and left the red wire from the junction bolt on the right fender disconnected from the battery then the alternator will not charge the battery nor will it run anything on the truck and the battery will soon be dead.

I suspect that the voltage regulator is stuck closed or shorted to ground which would blow the fusible link. If you look at the junction in the diagram I posted you can see how the alternator, battery, and the cab wires join. This allowss the battery and the alternator to feed the truck circuits and also allows the alternator to charge the battery via the red wire that goes back across the radiator to the junction bolt on the right fender, where it joins the fusible link to connect the battery into the circuit.