Disconnect that wire at your own risk- - - - -I've seen voltage spikes on an oscilloscope in excess of 100 volts just as the connection is broken. Solid state voltage regulators don't like those kinds of voltage transients. Simply turning high beam headlights on and off and/or running high current draw accessories like the heater blower with the engine not running should show ammeter needle deflections without putting your alternator in jeopardy.
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!