Installing third battery 1987 weekender 300

[William Carrier]

I purchased a third battery to hook up for a back up. I have been running with just 2 batteries. One is for the starboard engine and also runs the house and the second is for the port engine. The third battery has a spot to sit in the middle and I want to connect it to the house battery. Is it as simple as cabling the two together? Do I need specific cables? Do I need to run a switch to the helm? Currently I have a switch on the helm that will connect my 2 current batteries together so if one dies I can jump it off the other to get engine started. So would this third battery then be connected to both of the original batteries if I put a new switch in? And how would I do that? Thanks in advance.

 

[scoflaw]

That simple, tie the 2 together, you don't need a switch