Alternator problem..?

[VetteVet]

From what I can gather you have replaced the original alternator with another externally regulated higher amperage version. It would have been much better to get a 12 SI model internal regulated one or a CS version modern style and eliminated the external regulator.

Here is the original 64 wiring of the regulator and the alternator with the engine compartment wiring for added benefit. I see you say the wires from the loom are blue and yellow. The original wires were blue and white so make sure that the blue and yellow wire come from the voltage regulator to the alternator from and to the correct terminals. They probably do since it was charging on the old alternator and the yellow wire is probably replacing the white one.



Here is a crop of the diagram for better visibility


Notice that the white wire from the regulator goes to "R" and the blue wire goes to "F". Make sure the regulator and the alternator are grounded and grounded to each other.