Diagnosing high voltage

Checked those connections. They look good.

With key on, engine not running, my voltage at the ballast and voltage regulator is 2.0V, at the alternator it’s 2.6V, so I think those connections and numbers are ok.
You car going to have to define this. You measured from where to where?

If you measured from ballast to ground, "that's very low" (should be "same as battery)
If you measured from ballast to battery PLUS, "that's a lot" (a lot of drop)

"The path"

The path for the alternator field is 12V from the blue wire, from the ballast junction supplied to one field--either field---------through the field, out the second brush ---to the green field wire and back to the VR

The VR in essence controls "the amount of ground" the field sees to regulate field current. (It actually pulses so it' s a matter of duty cycle) this is how the VR controls alternator output-----a "harder" ground for more field current= higher output from the alternator

THE FIELD CIRCUIT might have a ground, either shorted green or shorted brush holder, causing the alternator field to see full current through the field, and max output.

Could be bad VR, and in rare cases, bad battery

Again, your voltage readings are confusing. Might still be a voltage drop problem