Help with Volt Gauge flicker.
.. my best guess is the MSD causing some kind of feedback or surging thru the harness
This is MOST probably exactly what happened. Even MSD, on their own site, warns against stuff like false triggering. That is, the MSD produces so much spark energy, that improper wiring "dress" can cause the MSD to "trigger itself."
This is not of course isolated to MSD. In this day and age of microprocessors, magnetic triggers and other sensitive circuits, fairly common.
You need to keep trigger (such as distributor) leads short, dressed close to the vehicle body (ground plane) and twist the pickup wires.
If you are old enough, you remember TV twinlead? You used to twist that to resisto noise pickup. In today's world, ethernet (Cat5 and other) cables do the same thing......tight twists in the pairs to reduce signal cross over.
