All or nothing alternator conversion

Reality wins, it is often measured with meters. To help with your theory, old style regulators energized the field wire, when IGN voltage senses too low, the other field connection is internally grounded. The new style regulator/alternator grounds the field terminal, so the other field terminal is powered by IGN circuit. Current flows in a load when voltage exists across it. Since the new style regulator pulls the field to ground to increase field, grounding the the terminal results in both terminal at the same potential, no field current, nor generation. Think of the field as a light bulb, how to complete an electrical circuit. If both terminals are grounded, nothing happens, if both are at powered at same voltage, nothing happens, if one terminal is grounded, the other powered generation happens. A meter can measure the field voltage, hence it does not have to be a mystery.