[VetteVet]

I'm working a similar post where the engine is running after key off but no battery drain. I think you might have the same type problem but a different diode in the alternator is shorted through and allowing battery current to go to ground. The other on is a diode that allows current to go back to the ignition switch.

The test you did on the charging post to ground on the alternator body is correct but you may have a bad diode on the small wire terminals 1 or 2.

My alternators tested 40 to 50 ohms both ways on the no 1 terminal and showed varying resistance on the no. 2 around 18 ohms one way and higher the other. This is with all wires to the alternator disconnected. If you get zero either way on the no. 2 you've probably got a bad diode. It can still charge at 14.5 volts but will drain the battery over time. Did you test for drain between the negative cable and the battery post? You should not get over 3 milliamps. That's .003. Make sure you have all the lights off and the key and no other draws on the system.