Setting up dual batteries (with switch)

[Pretzil]

My boat has and has always had the batteries set up on a dual battery isolator switch with the options 1, 2, both, off. A couple of months ago my dads cars battery rooted itself and he jumped into the boat and took one of the batteries. Since then we have been running on 1 battery but I just bought him a new battery and got the marine battery back.

The problem is that I never took much notice of how the batteries were set up and now I dont know how they go back.
The switch has two red cords and one black cord coming out of it along with a black connecting lead that was somewhere else in the set up. I would assume that each of the red cords would go to each of the positive terminals and the black joining lead that was there would connect the two negative terminals to each other with the black lead from the switch connected to one of the negative terminals. Would this be correct?

I would just try it but dad tried something the other day and it sparked and one of the bolt on terminals melted when we turned the ignition. So, needless to say I dont want to do the wrong thing again incase I fry something else

Also, I know this topic is probably somewhere in the past forums, I have had a look with a couple of search terms and couldnt find anything that answered my question.

Any help would be greatly appreciated.
Thanks

[sparkyice]

the way you describe hooking up the red and black cables sounds correct.
this is considered a parallel circuit.
the black cable is common to each battery and the frame of your alternator.
the reds would be selected by the switch as "A", "B", or both,"A+B" together going to your starter, electronics, etc.
make double sure you didn't reverse polarity on one of your batteries.
leave the black cable unhooked and swipe it quickly across the neg. terminals of each battery, without making a solid connection.
a little bit of a fuzzy spark might be normal if you have something turned on.
if you get a HOLY S**T!! spark, you've got something backwards, or a dead short somewhere in your wiring harness.

do this in a well ventilated area.

make sure there is no fuel vapor in your boat

it is tough to make a call without a schematic or by looking at the actual wiring
also, with twin batteries wired in parallel, the weaker battery will drain down the good battery. if the weak battery were nearly dead, it could draw enough current to make things things hot and melty.

why did pop's battery die? if he has a charging problem with his truck, he might have drawn down your marine battery too.

batteries have alot of energy contained in them, they can and do blow up, and can cause fires in wiring harnesses. if you have doubt about your aptitude, see a mechanic.

good luck, and tight lines,

joe