I don't think Delco ever made an OEM alternator that was designed for 1 wire operation. If you have a real OEM Delco 10si or 12si alternator, or equivalent, it should always be a 3 wire. However, if you have a Delco that was converted to 1 wire it would have a self energizing regulator.
These links explain what regulator is used in a 1 wire alternator.
http://www.purplesagetradingpost.com...o/onewire.html
http://search.waiglobal.com/partnum.aspx?part=D10SE12
Bruce