1965 Dart Charging System Question

Hello everyone,

I've been fixing what isn't really broken today, and I have a few questions, just for the sake of my own education. I replaced a worn ignition switch, and I took a few voltage readings at various places. Here is what I found:

Key on, engine off:
Battery: 11.8V (this ranged up to 12.2 after I let the car run awhile)
VR at Ign.: ~10.7V
Ballast Resistor: ~10.7V
Ign. Switch Hot: 11.8V
Ign. 1 at the switch: 11.8V
Bulkhead connector inside the car: 10.7V

Key on, engine running for 20 minutes:
Battery: 14.3-4V
VR at Ign.: 14.0V
Ballast Resistor: 14.0V

I didn't check the rest with the engine running, but I think it's clear that I must have a corroded wire or something between IGN1 and the firewall. What I don't get is why the voltage drop is so much lower with the engine running. Can anyone shed some light on that?

Is there anything else between the ignition switch and the firewall? I actually changed out the connectors and a length of wire that seemed a little brittle at the switch, but that didn't change anything. It's obviously not something to lose sleep about; I've been driving it this way for years. I'm just curious at this point; it never hurts to learn something new. Thanks!

Aaron