How much voltage?

Test w/ a multimeter. With both field terminals disconnected, you should read >1000 ohm to BATT- from both. A 1965 alt should have a single field terminal. The other brush is grounded, which is why it won't work w/ a 1971+ Vreg. Those use "low-side switching" vs "high-side" in your car. I use a later square-back and later Vreg in my 1965 Dart.