Alternator swap driving me nuts!

Try running the engine at fast idle and measure voltage both at the battery and at the alternator stud. Maybe you have an open/ bad connection in the ammeter/ charge circuit

If the two voltage readings are no more than say, 2-3V apart, and should be less, then you can test the full output of your new unit by disconnecting the green, and jumpering the alternator field terminal to full 12V You can jumper right to the alternator output stud. Be careful, it is always hot to the batter. Watch the RPM, and battery voltage, and if it charges, don't let RPM cause it to climb over say, 16V With headlights, heater, you should be able to bury the ammeter.

If it has two field terminals, and can both be INSULATED, consider converting to the 70/ later VR. All you need is the matching pigtail and connector, and add one more wire.