take the feild wire off the alt- then check the alt terminal for the feild wire to ground- there will be some resistance due to the end of the field coil to the case of the alt.- simce it was checked out ok- I think it is good. the reg. sends out voltage to the field coil to excite it to produce power.use a volt meter accross the battery and wtach-then with the field wire off and the car running- take a jumper wire from the large power wire and touch it to the field wire- you should be producing power. if yes with about + 13-14 volts at the battery- the alt and wiring is ok- look at the reg. make sure it has a good clean ground behind the mounting bolt.
Something extra to do is to add a braided ground strap from the reg.'s mounting bolt to the rear head bolt of the engine.

John Mac