Novo,
Check Bluesea systems website, for their pdf directions. Different manufacturer, but the routing is the same. I do know that if you're using a "smart charger", the charger can be wired to both batteries, and the selector switch wiring can be independent of that. I've done alot of research on this; and would consider investing in an ACR and automatic switch rather than the manual. There's an "add a battery" kit that contains both..
Good luck!
Jim