Thats kinda what I was thinking. According to your tests, the alternator should be charging. Your L circuit is what tells it to charge.Is it just me or do others also see a grounding issue with either the alternator or the engine?
A simple test you can do is compare battery voltage terminal to terminal, vs battery positive terminal to engine body. You should see less than .2v difference. If your numbers dont make sense or are way off, you have a engine grounding problem.
Another test you can do is grab a jumper cable, and simply connect it from the alternator body, to the battery negative terminal, then check your charging voltage.