Ed
Hooking the exciter circuit to the S terminal will work in theory but I don't recommend it because any solenoid will generate a fairly high voltage spike in the circuit when B+ is removed and the field induced by the coil windings brakes down. That spike would most likley cause a failure of the diode triode for rectifier. I recommend using a diode and an inline 10 ohm [2 watt + ] resistor installed in series in that wire, [that resistor isn't required for the alternator to actually operate, but is put there to protect the diode trio inside the alternator from damage due to a power surge. One other thing you might want to consider is the sensing wire. You often see the B+ and the sensing wire joined at the alternator but the best way to do it is to go to your power distribution ( fuse box) and tie in there. That way you are sensing demand of your electrical components so the alternator can better compensate for the various loads and not just sense battery state. I usually use an 1N5408
Moose