1965 Dart Charging System Question

Aaron65 said

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?

Click to expand...

Two reasons.
a. Voltage drops with increasing current through a resistance.
b. When the engine is running, power is coming from a different source - the alternator. Therefore current flows through different path for some of the journey.

There is another difference related to both of the above. Most devices draw more current when given power at a higher voltage. The battery only had enough charge to provide power at 11.8 Volts. In your running test, the alternator was providing power around 14.4 Volts.

However in your case, the voltage drop is greatest when powering from the battery.
That would suggest only b - the route is the cause.
To really know if the drop larger or smaller, measure the voltage at the alternator vs. voltage at the ignition wire.