For more detail, I have about 50 kOhm resistance between the 12V pole and the case of the rectifier/regulator, where I would expect infinite resistance. It's enough resistance that a continuity test fails, but clearly there's voltage going through there, and I think that's bad. Just need someone to confirm.

Note: I understand the basics of electronics, and what this little solid state device supposed to be doing at an academic level, but maybe this is working as designed and I need to find another reason for the power drain.

 

The resistance if probably a red herring.

At 50KΩ ant 12V, you're drawing less than a milliamp. It would take an eternity to drain the battery.

 

clip a test light between the battery terminal and the battery cable, as you did with the voltmeter. Turn the lights out in the garage. If you see any light whatsoever, you have a drain. In a bone stock bike, only the rectifier has access to the direct battery current , all else is switched through the key. If the bike is bone stock, and you see a light, the rectifier is either wired improperly or has a bad diode

 

How many wires connect to the regulator? Assuming it includes the rectifier, I count two for the stator, one ground, and one output to the battery. Any more?

As was stated, 50kOhms will take a long time to run a battery down, and, since it has a measurement circuit inside, there has to be some leakage through the regulator.But, if you have a fifth wire for voltage monitoring, it is best to connect that to the key switch output, so you have no leakage at all.

It occurs to me that you should set your meter to current, and measure the current through the regulator to ground. Then, ground the regulator, disconnect the battery negative and measure the current from that cable to the negative terminal. They should be the same, and very small, but start with a higher setting on the meter first.