Would like to install a small solar panel but our battery wiring seems odd.

[Cthoops]

Mr. cthoops and I are electrical newbies but learning bit by bit. This is our first boat with two batteries and a Marinco switch. The batteries are both AGM 85 amp, and the switch is your standard 1/2/both/off Guest.

On the back of the battery selector switch we have three cables going from the left post (the one directly behind "2" on the front) - a skinny red one connected to a Blue Sea on/off switch (which appears to control the VHF and a cigarette lighter), a fat red one leading to the alternator, and a skinny red one leading to the ignition switch. The center/upper post (the one directly behind "both") has a fat red cable connected to the positive on our #1 battery. The post on the right (the one directly "1") has a fat red cable leading to the positive on our #2 battery. See picture below.

Shouldn't the wire leading to the alternator be hooked up to the center post, which I believe is the common post (since it is the one directly behind "Both")? That way the alternator would charge both batteries? Is there supposed to be a positive and a negative coming from the alternator (we have a single-cylinder Yanmar SB12 - original engine)? Also, to make it more intuitive, shouldn't the positives from battery #1 and #2 be connected to their corresponding posts on the switch (instead of the common and the post behind #1, respectively)?

As for the batteries, they have the following wires: Battery 1 + is the cable to the Guest switch and a Marinco battery direct connect which has the positive for our bilge pump and our Nature's Head fan; Battery 1 negative has a cable leading to the negative on Battery 2, and the Marinco battery direct connect with the negatives for our bilge pump and our Nature's Head.

Battery 2 + is the cable to the Guest Switch, and Battery 2 negative has 4 cables/wires: a cable from the Battery 1 negative, a wire leading to the negative on a bus bar, a wire leading to the Blue Sea switch, and a cable leading to the engine - I believe that's the ground wire, although it's been a while since I've looked at it. Maybe it's the negative from the alternator?

As best as I can tell from reading and researching, if the negative running from B1 to B2 is connecting the ground wire (instead of the negative from the alternator), there really should be two cables running from the ground to each negative post instead. Correct?

Finally, if I'm right about the above and we make those changes, and then run a battery cable between the positives on Battery 1 and battery 2, and another cable between the negatives on Battery 1 and battery 2, then they'll be wired in parallel. Then when we hook up the solar panel, we can run the positive from the controller to the positive on battery 1 and the controller negative to the negative on battery 2, and the solar panel will charge both batteries, correct?

Any help would be extremely appreciated. Thank you!

[smac999]

Originally Posted by Cthoops

On the back of the battery selector switch we have three cables going from the left post (the one directly behind "2" on the front) -!

the posts will be labelled on the back. you may have to move the cables to see. where the posts are located means nothing.

where is you "engine (starter)" pos? are you confusing alt with starter?

[Cthoops]

Originally Posted by smac999

the posts will be labelled on the back. you may have to move the cables to see. where the posts are located means nothing.

where is you "engine (starter)" pos? are you confusing alt with starter?

Thanks. I magnified the photo on my computer screen and it looks like I can slightly make out some lettering on the back. We'll be on the boat tomorrow so we can confirm, but it does appear that the alternator/starter/BlueSea cables & wires are on the common post, with the battery cables on their respective 1/2 posts.

If I traced them correctly, the alternator and the starter cables are both on the common post.

[Stu Jackson]

Installing Battery Selector Switches (the "posts" in the back don't physically match with the switch positions on the front) Batteries and a factory (?) mis-wired battery selector switch

These may help, too:

Basic Battery Wiring Diagrams This is a very good basic primer for boat system wiring: Basic Battery Wiring Diagrams

This is another very good basic primer for boat system wiring: The 1-2-B Switch by Maine Sail (brings together a lot of what this subject is all about)
1/BOTH/2/OFF Switches Thoughts & Musings | SailboatOwners.com Forums

The Short Version of the 1-2-B Switch Stuff: Electrical Systems 101

[wooden head]

If you wire up your batteries in parallel you may as well get a two position switch as you will only have one bank of batteries. That's all well and good as long as you dont run down the batteries and plan on starting the motor.

[wooden head]

A single wire alternator will ground through the engine block.

[jeepbluetj]

As mentioned above - where the terminals are have nothing to do with the switch. A few min with an ohmmeter and you could trace it all out pretty easily.

The links Stu posted are good.

[Cthoops]

Been offline for a few days. Thanks, Stu for those excellent links and to everyone else for the suggestions/advice.