a pictures worth a thousand words

[phatdaddy]

Also might want to wire in a float switch directly to + side of battery with an inline fuse, so bilge pump is active even with the selector switch in the off position.

[Lance Pearson]

I had decided not to put a battery switch inline as some haven't with one battery but remembered you can add a simple switch which mounts to the negative battery post and which the negative cable attaches to it. When you want it off to the boat just turn the knob on top and it breaks the connection. Cheap, simple and better than leaving something on inadvertently when you leave the boat for a while and it's not in a slip, etc.