As a follow up, I just finished replacing the voltage regulator, and the harness that runs from the alternator to the starter (944 607 029 01). I think the reason why the alternator wasn't putting out any voltage, is that the brushes (a part of the voltage regulator) were worn down enough, that they were being held back by their leads, and were not making contact. As soon as I turned the engine on, it was charging at 14V again, so that's great!
As for the harness, I could feel that the old one was crunchy, so I sliced it open, and it was terrible! Lots of moisture, both wires exposed, old cracked casing just piled up like rubble. I can imagine this could be causing other electrical gremlins in this state, and I feel really fortunate my car hasn't driven off by itself yet.
Anyone who hasn't replaced this wire should make it a priority...at this age, I can't imagine any of these harnesses are in good shape. Brittle from the heat and age, corroded from the loose housing, looped perfectly to catch and keep all moisture. I was able to do the job in about 2 hours, and didn't remove anything other than the lower shields. It's certainly a bit tight in there, but workable.