I agree with HambBurglar on the advantage of a 3-wire over one wire.
The GM late '60s/early '80s 10/12SI alternators are the most common/popular, either original/rebuilt GM or brand new aftermarket from several companies.
The DA plug connects the two rear spade connections: #1 goes to the ignition switch through a diode and/or an indicator light (to prevent run-on with ignition off) and #2 goes to the main voltage distribution lug, the same location as the main output wire.
Open this link and learn more about these alternators and more.
MadElectrical.com - Mad Enterprises