Engine Stalls Out in Drive when Headlights Turned on or AC turned on

[Tampa Stang]

Help! I've got a 1965 with a 289 automatic. Car has PS, disc PB, and AC. Car idles fine in park from cold start and after it's warmed up. Idles as it should in drive as well. After the motor warms up (around 15 minutes) if I turn on the headlights it wants to stall out and has rough idle. Seems like there's a "miss" in the idle and sometimes it will stall out on me. The car starts back up again. If I turn the headlights off the car idles fine. If I turn the AC on it will stall out as well.

I've already replaced the voltage regulator, checked the plug wires, distributor cap, changed out the negative battery cable and checked for vacuume leaks.
What are some other ideas I'm missing?

 

[65ShelbyClone]

Did you check the battery voltage when it's running and lights are off? How about running with lights on and rough idle?

 

[wicked93gs]

Idle RPM with headlights on and off?