squareback alternator wiring in pre 70 car issue

Beware! Using a wire to jumper on a regulator may result in damage to regulator or other problems.

Early style regulators energize the field with (IGN) power with relay contacts or transistor as necessary, the other field connection is ground. In the early alternator, the field brush was grounded to case. The newer alternator needs one terminal grounded, the other goes to field (FLD) terminal on early regulator.

The later style regulator pulls the (FLD) to ground, with transistor to excite the field, the other field terminal is connected to (IGN) for power. The field is just an electro-magnet, it spins, and creates voltage in the stator windings. The intensity of the field is controlled by the regulator looking at the IGN voltage. In both circuits, ground at the regulator case is essential.

The problem of over voltage in your first post, often happens when the alternator output to battery, has voltage drop to (IGN). The regulator works to make (IGN) correct, that is why a voltage reading of (IGN) is important, for trouble shooting.