If the grn wire from the alt is disconnected from the harness, IT's not grounded. The field is a coil of wire, an electromagnet, with 5.4 ohms resistance. When it is disconnected from ground, the coil is an open circuit, with no current flowing, and reads the same volts as the other end of the coil, the wht wire. The reason I didn't think jumping was indicated in your case, was your earlier reports of no voltage difference, running or not, between the blk and wht terms at the reg, with everything hooked up normally.
For the record, you do not have problems with blowing fuses, or the battery going dead over night, right?