'66 Valiant Weirdness

My '66 Valiant 225/904 has been having some interesting issues. Apparently I messed up by trying to fix something that wasn't really broke.

I recently got this car back after 10 years of neglect by the PO, so I've been working my way around it making it a dependable driver again. I noticed that the lights were flickering a little bit and after a bit of reading I figured I should go ahead and replace the Voltage Regulator and Alternator, since both appeared to be the original parts. Replacements on RockAuto were very reasonably priced, so I ordered them up (Standard Motor Products PN# VR101T and Pure Energy PN# 7000112). After starting the car the first time with the new parts installed, the needle on the Alternator gauge was jumping around a little bit, but seemed to even out after the car warmed up.

The next day I installed one of these Electronic Distributors and at first everything seemed fine, the car was running excellent with that new ignition system. Then things started getting kinda funky. The Alternator gauge started bouncing around very erratically, even at idle. Didn't seem to matter how much juice I was using as far as the lights, stereo, etc. This first video shows what it was doing while I was sitting parked, engine fully warmed up. You can hear the idle speed changing on its own and the lights getting brighter and dimmer in sync with the gauge.



After that I put the original VR back in, mostly out of curiosity. It was acting like this and added stalling and subsequent hard starting to it's list of misbehaviors.



I'm a decent mechanic, but I'm a **** electrician. Do I need to make an adjustment to the Voltage Regulator? Should I start checking grounds? Hire a witch doctor? Hoping one of you can help me understand and fix this. Any help is appreciated, thanks in advance!