[dcb]

If you have an external regulator than you switch off the field lead.

If you have an internal regulator then you may have to dissect it a bit and bring out a field lead to a switch.

But it will be completely unloaded if you make sure the field is de-energized (the field is the rotor in this case, connected via the slip ring brushes). The regulator *shouldnt* self destruct if it loses field continuity, but can't guarantee it (could be some dumb voltage regulators out there I recon).

You can also put a hefty switch in line with the alternator output lead (the thick one) but the alternator will stay self-excited and take a little extra power until the engine comes to a stop.