Do you have an ammeter or a voltmeter? Which alternator are you using- - - -the internal-regulated 10SI or the earlier model with a remote regulator? Neither one should function without the plug installed, although some of the 10SI models can get some feedback to the internal regulator through the diode trio and appear to be charging.

What was the voltage at the battery terminals? If the alternator is actually charging, it will be 13 volts or more.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!