Great source for electrical help – Colin at Townsend Electric, very nice guy and super knowledgable
Port Townsend Electric
The starter (2 part) and the pre-heater both use 24 volts. Other things (instruments, etc) use 12 volts. (I suggest you use the separate (cheaper) car battery for bilge pump and all house lights, instruments, etc.
Here is a diagram of how to hook up 12 volt wiring vs. 24 volt wiring with the batteries connected in series.
The solenoids at the back of the battery compartment control the 2-part starter solenoid which is that giant green gizmo underneath the two solenoids (wiring diagram to come) and the pre-heat unit
Follow the wires to the starter
CLICK here FOR STARTER WIRING DIAGRAM
(for sometime in the future) The switch hanging out by the 8D batteries (but not attached) goes to the starbord side lazarette (where the lead slugs are) – It would be good to install two 6volt batteries (for maximum amp hours) and use for house lights, etc.
When installed (12 v I believe), you can charge the small house batteris from the big 8D batteries while underway using that switch. Flip it off when batteries are charged to prevent discharging large batteries.
The alternator to charge the batteries while underway is mounted above a large pulley mounted to the flywheel at the forward side of engine.