I have a 2006 Mainship Trawler twin engine Yanmar. I just installed a dual out put solar controller plus 175 watt panel because I keep my boat on a mooring and some of the parasitic charges keep running down my batteries . I am trying to figure out how to choose the priority batteries to charge. The controller defaults to the position #1 when there is not enough solar to charge both banks. I have three 8d batteries (two outboard of the starboard engine not in parallel as far as I can see)two cut of switches marked port engine and starboard engine. There is also a third cut off in the bilge area that cuts off another battery located outboard of the port engine. There is a separate battery for the windlass and the generator aft with its own cut off switch as well. When I cut off switch to port battery both engines still start. When I cut off port or starboard switches corresponding engine won’t start. When I remove cable from one of starboard batteries with both port and starboard switches in the on position there is not enough power to crank either engine but they are not visibly in parallel. This is confusing me , I don’t know what “house battery”is because when I switch off the single battery outboard of port engine with the switch in the bilge I still have house power to some items(not fridge). The owners manual is of no help. Does anyone know if this is the original configuration and have a schematic? In the mean time I have connected the priority charge to the two batteries that seem to be somewhere parallel that start the engines and do run a couple of bilge pumps.