Disconnecting the field exitiation wire should cause no damage. Alternators with internal regulators need only a brief jolt of current after the engine starts to energize the field coil. Once this happens, the half-wave rectifiers (diode trio) take over and produce current for the field directly...
Regarding testing alternator output: Shorting an alternating current generator (alternator) output to ground will result in serious problems. Generator output can be tested in two ways. A carbon pile resistor or other resistive unit is connected in parallel with the battery with the load applied...
