Actually, that would only happen if you still had the internal regulator since it samples its output voltage to see what it needs to do to change the output. With no regulator, once the 12 volts is cut to the field, it is dead. there are no wires feeding the field besides your 12 volts from the ON switch. The field coil is nothing more than an electro magnet turning inside a three phase coil of wires. once the electro magnet is shut off, there is no more magnet to make power. The field requires about 10 amps to run, so I doubt there would be enough residual magnetism to really make any power. I guess it is possible though. I guess I could try to put a volt meter on the alt and turn the field power off and keep the engine running. that would be the way to test it out.