I don't know. Try eliminating whether it's an engine / carb /tune problem, or electrical.
One thing you might try is to "rig" a meter that you can monitor while driving, with a wire strung so you can move it around. Monitor the battery. Do some test drives with the regulator unplugged. That is, run off the battery. Move the voltmeter to the "high" side of the ballast resistor, that is, the wire coming out of the bulkhead feeding electrical loads / ignition under the hood.
If that indicates trouble, try to figure where the drop is, IE bulkhead connector, ignition switch, or the switch connector.
Some of this you can check in the garage. "Walk" the multimeter from ignition to bulkhead to ignition switch, etc, to wherever the feed comes from the battery.
No1, 2, 3 suspects in no particular order.........
Bulkhead connector problems
Ammeter circuit or what's left of it
Original ammeter splice in the black wire originally to ammeter in the inst. panel.
Ignition switch or switch connector
If none of this shows anything, might be an intermittent right in the ignition system.
"How does it act" for idle? If the idle is too lean, etc, you can have similar problems.