need understanding of dual batteries at entrance step...batteries were missing when I acquires coach and now I need help to understand isolator/switch connections. Presently there is a what I'll call a starter solenoid, with a S and an I terminal. My confusion comes, as to how do I connect two batteries to that type switch, old school type Ford fender mount solenoid? Do both positive leads from batteries go to same large terminal? I do also have a working generator. Please help me, thanks. Picture or drawing would be really good.