[RichardJ]

The first drawing below with the external regulator is very little different than the drawing for the 10SI internal regulated alternator. All they did was stuff the regulator and a couple pieces of wire inside the alternator case.

The exciter wire from the voltage regulator, whether the regulator is on the radiator support or inside the Alt, goes to the idiot lamp and to the ignition switch. That wire going to the ignition switch is actually a resistor wire, not a free-standing resistor component. That resistance wire is in the harness, whether it has a idiot light or an Ammeter gauge.

Unless the harness has been altered, you do not need to add a resistor. It's already there.

VetteVet was talking about adding a different resistor if you were going to install a CS alternator.

The wire on the engine side of the firewall that goes to the regulator is a standard copper wire.