I've got a solid ground. The 'dancing' was happening with the charging system connected too so I tried disconnecting it to see if that was the cause. Still have the mech. regulator, new rectifier.
Maybe I'm not understanding how the regulator works - does it pulse often in short bursts or is it a more slow, prolonged charge? I was under the impression the battery would drop below 13.5, the regulator would turn on for a minute or two and then turn off.
The bigger issue here is that I can't get a solid voltage reading to adjust the reg so I've been erring/adjusting on the side of not charging it enough.