Jumping in here although you likely solved your issue by now.
In my experience, many folks tend to jump the gun coming to conclusions and replacing parts without doing careful testing, troubleshooting and problem isolation. This has proven to be true with most any technology not just Harley charging systems.
Glad to see you are indeed doing component level testing and intelligently isolating the bad actor.. I'd also add that most of the time a problem will turn out to be something ridiculously simple and often due to careless or long deferred routine maintenance.
In testing charging systems (in pretty much any vehicle) I put a VOM on the battery. Motor off the charge should be in the 12+ vdc range. It it's way low the battery could be too far gone to even take a charge.
All of my vehicles are always on a tender when not in use so if I have a weak battery problem I know about it pretty quickly. If in doubt, throw a load tester on the battery. They are dirt cheap at Harbor Freight.
Start the motor. If it fires up this is obviously good. The voltage should jump up to the 13+ vdc range. Measure the voltage from the battery posts AND the connections to the battery. If the voltage doesn't increase at all then you pretty much know where to go from there. Stator is easy enough to check as you know. So long as no one has been monkeying around inside the primary stators tend to be extremely reliable.
Regulators can fail in several ways. One is where one of the diodes has failed so instead of outputting clean DC it outputting only 50% of what it should be. This is very easily viewed on an oscilloscope. Yes, most people don't have one. Just be advised that just because the regulator is outputting power that does not mean that it's clean 14 VDC. If a diode (rectifier) is blown the actual DC output will be ~ half that.
Of all the components that could fail the regulator is the more likely and least expensive to replace. Many times a regulator will fail due to some event like creating a short circuit when replacing a starter. Ask me how I know....
But bear in mind that a bad connection somewhere in the circuit will cause the same symptoms. I did read that you checked that but perhaps not carefully enough? Very common for there to be a poor connection on one of the battery terminals. Especially true if you have more than one lug connected to either battery terminal.
Really clean up those lugs, terminals and connectors and use a little conductive grease on them when you reconnect everything. Give each wire a tug to ensure the crimp is tight.
All of the above is worth doing even if it doesn't resolve this particular problem. Seems like I've spent half my life troubleshooting bad grounding problems in anything that runs on electricity. Hope this helps.
