voltage on the ballast res

The low reading you are getting on the "dark blue" coming OUT of the bulkhead from the ignition switch is an indicator of TROUBLE. You have a voltage drop in the bulkhead connector/ ammeter wiring/ ignition switch/ ignition switch wireing.

(Before I recently did a partial rewire on my 67, it had a ONE VOLT drop between the battery positive post and the dark blue IGN source at the ballast.

THIS ALSO WILL CAUSE overcharging, because this is the sensing voltage for the regulator.

Let's say, like me, YOU HAVE a one volt drop. This means that if the regulator "is correct" and is TRYING to regulate at 14V, it "sees" 13V at the "dark blue" because of the troubles in the harness/ bulkhead.

BUT IT IS REGULATING at 14, so it RAMPS UP until that 13V is 14 AT THE DARK BLUE. But because there is a ONE VOLT drop between there and the battery, the battery sees 15 volts!!!

First thing I'd do is pull the bulkhead apart and inspect clean, then consider doing an "ammeter bypass" and clean and inspect the connector for the ignition.

I went further. On my 67, I installed a fuse / relay center out of a 90's Caravan, has several fuses/ relays inside.

I used one relay for "ignition run" IE ignition and alternator field, one each for low and high beams, and a third for the pump. I "threw in the towel" and converted the ammeter to a Sunpro voltmeter, and now the voltage in the system is pretty much "perfect."

The bulkhead has been eliminated. I just gutted it, and fed the new wiring through the connector holes.

(I do need to crawl in there and seal 'em with RTV)