Battery Voltages vs Capacity
Well - long story - try to condense:
Spent the better part of a day tracing wires on the boat. Discovered that someone had attached the CD Player to the starter battery bank - no fuse, no nothing. So that was the source of the continuous drain on the starter battery. Of course, the CD player is attached to the radio/stereo which was attached to the house batteries. Thus, power was going from the starter battery through the CD Player through the stereo and bact to the house bank. No good. Interesting voltage readings on the various wires.
Then, in the process of debugging, found that the ST-50 seatalk power line was attached (and jumpered) between the wind, depth, and speed on off switches on the 12 volt panel. Of course, each of these switches was on a separate circuit breaker. So in essense I had three circuit breakers in parallel if I turned on all of the switches at the same time. Not good. But the best was, the autopilot end of the seatalk cable was attached to the course computer with about 12 AWG cable, the other end of the same run was attached to the depth gauge with about 22 AWG cable. (think on an extention cord with a male plug at each end, and the outlets in the middle) So, if you turned on the instruments by turning on any one or more of the depth/wind/speed instruments you got a .4 Volt voltage drop at the autopilot. If you turned on the autopilot end, you read near battery voltage. So, net net, we were trying to run the autopilot on a 12 ton 42 foot sailboat through 22 AWG wire. No wonder the autopilot complained "low battery" all of the time!!!!! Disconnected the wind/speed/depth end, will give it a sea trial tonight and see if the autopilot works for more than 30 seconds!
And ... (yes, there''s more - it slices, it dices!) I discovered that the reason that the chart plotter autopilot mode did not work was that there was no NEMA circuit to send sentences from the chart plotter to the autopilot. There was only the connection in the other direction - e.g. to send navigation data to the chart plotter. Ran out of time - but one more pair of wires and I should be able to point to a destination on the chart plotter and have the autopilot steer to it. That would be "all good."
Of course, after spending the better part of the weekend debugging the electrical systems we tried to clean up after dinner and could get no fresh water in the sink. Discovered that the fresh water pump had thrown its belt as the pullies were out of adjustment. As they say, win some, lose some. Went down and fixed the water pump this morning. But, what a bummer after the high of getting a handle on the electrical problems to have yet another problem exhibit itself.
Thanks to all who contributed ideas. The lesson learned is - don''t trust anything on a boat you have purchased to be done correctly. Work you way through each system until you are sure they are OK.