I charged the battery to about 80% and then started up the car without the volt gauge hooked up to the MSD 12v source wire.
At 1200rpms high idle, the battery voltage guage and the ammeter still fluctuated but not as bad. The voltage guage showed 14-15 and the ammeter moved from straight up to about 1/4" to the + side. It never showed discharge.
At 950rpms, the voltage guage showed about the same and the ammeter moved from straight up to about 3/8" to the right. So it shows worse still at a lower rpm.
The interior dash lights were changing brightness up and down too during the idle time but not at high idle.

What if the issue is something inside of the car and not in the engine compartment? Could a loose connection anywhere in the car cause the ammeter to fluctuate on the + side? If so, since the dash lights are fluctuating, should I track down that circuit to look for an issue?

Thanks again.