[Kurt in NJ]

3 brush generator needs a battery to control voltage, without a battery the voltage can go over 45 volts and it will fry, the smoke will come out of the windings This is because the third brush powers up the fields. They say these generator need output grounded, a 2 brush generator needs the fields externally excited there's not enough magnetic field for it to fry itself

Running the engine without coolant is a good way to start cracking