'66 Valiant Weirdness

Forgot to mention that when there is weirdness in the ammeter readings one of the first things I do after a quick visual check of the wiring is check voltage.

With engine running measure voltage at battery positive, alternator output and at or near the regulator input (aka ignition wire connection at the ballast or the regulator).
Knowing the voltage at these locations plus what the ammeter is showing for current to/from the battery helps make a complete picture.
I also check it engine off just to get a ballpark on the battery condition.