Couple Electrical questions
 

First question.

Do most of you running two batteries, 2 selector switches, twin engine, run a ground wire between the two blocks?

Also, I have new 100 Amp alternators. I would like to upgrade the original small gauge wire going from the alternator to the starter terminal. What gauge wire will support say 100AMPS?

My boat has a ground strap between the blocks. Almost forgot about it once when pulling the motors. Started to lift the boat up. Just a little - I realized when the crane needed more effort to lift the motor when the motor was already off of the mounts.

fixx
 

one switch 2 batterys,2 switches will support 3/4 batterys..the negitive i have one on each side and the two engine are connected at the back,then the ground goes to a gimbal housing bolt and a bolt on the trim tabs..if you have hyd steering i suggest to run a wire to those also which no one ever does..

8 gauge wire to the back of the laternator with a 100amp inline quick blow fuse attached to the spade on the output lug on the alternator..

http://www.ebay.com/itm/LOT-6-Marine...-/250420457971

I believe it is a USCG regulation to have the blocks physically connected by a common ground cable????? Reason being, if one of your batteries neg cable came undone and you'd try to start that motor, you wouldn't have a completed circuit. BUT, since liquid does conduct, a slight chance current would try to flow thru your fuel line. And that would be bad. The additional ground cable is a safety item that removes the fuel as a path for current to flow.
May be far fetched, but just what I learned (was told by a marine specialist that mainly deals with large off shore boats) last winter while researching rewiring my battery setup in my cruiser. Sounded good to me, so I left mine on.

According to an electrical wire calculator:
6awg can support 102 amps within an engine compartment if not bundled. May be safer to step up to 4awg
http://shop.genuinedealz.com/Store/Tab.aspx?tabid=2

Thanks for the info. Makes sense to me. Not sure what gauge the factory merc alternator power wire is, but I dont think its more than 12, maybe 10 gauge? I dont wanna melt the stock wire and start a fire!

good info Mike. Saw you called this weekend, i was out of town. I'll give you a shout tomorrow evening

Yep, wire is cheap. Boats aren't

Do you have the two batteries tied together? If so and if you ever run with the switches in the "both" position, then you really should install an isolator. Anytime I do a twin engine boat with only 2 batteries, I use an islolator. You can mount it anywhere you want and run the alternator wires to it, and then to the batteries. It will only allow the current to flow one way. Then there is no risk of overcharging one of the batteries or having the alternators fight each other.
Eddie

Mine has one switch for each engine? Normally, I run the starboard on "1", and port on "2". Appears to be factory fountain setup.

I am considering adding a extra "house" battery, deep cycle mounted using a isolator. Mainly to run the stereo while at the beach. I have a couple decent sized amps, and dont wanna keep running the starting batteries down, i hear they dont like deep cycling?