Have a 12v 55 Amp Delco 10SI 3-wire Alt with 4 inch +- belt pulley on my '47. Some here prefer a Ford unit but I have never had a problem with this Delco. My Alt came to me wired as a 1-wire set-up and (1) the alternator would not charge at start-up unless I raced the engine, and (2) my lighting was typically dim due to low SYSTEM VOLTAGE (not bad wiring, under-sized wiring or poor grounding). I corrected the wiring arrangement and immediately found that the 3-wire arrangement works better. Wire #1 being the output to the Batt terminal at the solenoid.... Wire #3 (system voltage sensor wire - usually white color) also goes to the battery terminal at the solenoid which allows the alternator to properly sense the actual SYSTEM VOLTAGE at its connection to the battery, AND allows the Alt to respond to it .... and Wire #2 (field wire - typically brown color) goes to the ignition switch via a 10 watt -10 ohm resistor (rather than a 1960's dash glow-light) which in-turn allows the ignition switch to "excite" the Alt into action immediately, even at idle rpms. (I bought the resistor at my local Radio Shack) I recommend searching other threads/postings at the various forums and exploring the internet regarding these concepts.
