There is virtually no way to short the alternator stud to the field so that is not your problem.
Under no load, there should be 12 volts on both terminals. With no current flowing, there is no drop across the field. With that test you have confirmed that your brushes are in contact with the field at least at rest. It could change when in motion.
Short primer on how the regulator works: There is a constant 12 volts on one terminal. On the other terminal the regulator supplies a ground through a pass transistor on the regulator. The lower the voltage on the system, the lower the voltage on the field terminal it is connected. If there is no current flowing through the field, as Dayclona mentioned, there will be no magnetic field developed, no screwdriver attraction, no voltage generated in the secondary. Generally the failure of the voltage regulator is the failure of the pass transistor. It opens up. Rarely, it can short to ground making the alternator run at full current, cooking the battery. I have only seen that once in 40 years on a Volare police car.
If you hook one wire to the battery positive and one to the battery negative, the only thing holding the voltage down is the battery so depending on its condition, thermal runaway can occur and voltages well over 15 volts can be generated.
Craig