So, I was a bonehead when I first tested the sense wire - the key was off. Doh!
After subsequently studying the diagram in the service
manual for the alternator it was obvious that the key had to be on. That crossed my mind originally, but finding the sense wire at ground instead of floating/open is what threw me. I turned the key on, the light came on and the sense wire was at battery level.
Starting the engine
, the voltage went to 14.5 then up to 15+. Voltage still fluctuates between about 14..5 and 15.5 at about 1 - 2 Hz. All connections seem to be clean and secure.
I went through several on-boat diagnostics and it seems to point to the regulator, so I pulled the alternator and am taking to an alternator shop. I will be disappointed but not surprised if it comes back testing fine telling me I still missed something.
I also checked the spec gravity of the cells. A couple seemed a little iffy. The alternator shop thought that the regulator is the problem, but also suggested load testing the batteries.
More to come,