Wiring a switch and isolator

hey all- just wondering if someone could double check this diagram and let me know if it looks right.

I have 2 interstate crank batteries, connected to an isolator and switch. Might be a bit overkill, but I have pulled up to the launch too many time and had a dead battery, so i added a extra spare, then I would have to crawl into the battery box and switch the wire to find out that the spare was dead...

Now I hope to charge both with the alternator of my 150 yamaha, hit the switch when it is back in the garage so my depth finder or radio dont drain the battery when i accidently leave it on for the next trip!

Re: Wiring a switch and isolator

Your wiring diagram is correct, and will work fine.

make sure all of your grounds are connected. including from Bat1 to bat 2

Re: Wiring a switch and isolator

Grounding both batteries together is OK??

Thanks for your help

Re: Wiring a switch and isolator

Absolutely. The only way that setup will work is if you ground both batteries together and to the engine.

Good luck with the project.

Re: Wiring a switch and isolator

You are isolating the positives on the batteries (using the isolator), and selecting which battery to use with the switch (or both)

You don't isolate the grounds, thus you connect them together.

If you were to not connect the grounds, and say connect the bat 1 ground to the system, when you switched to bat 2, you would not complete a circuit and you would have no power.

Re: Wiring a switch and isolator

OK, a little change after some trail and error this weekend, The line was to my GPS, not the starter.

I have one line coming out of my motor, obviously red and black...so the red (which I assume is the alternator and starter) is running to the in line on the isolator. This now feeds both batteries while the alternator is running.

BUT since the nothing brings power back to that line, I cant start the motor.
Is it ok to double back from the in pole to the feed line on the switch??

Re: Wiring a switch and isolator

I think if I understand you correctly, yes, but you want the big wires on the switch, not going through the isolator. the isolator is an add on. get the basics, and then add in the isolator.

Lets start with installing the switch so you can use your boat.

Big red from motor. Put that on "feed" for your switch.
Big reds from switch. put one on each of your batteries positive.
Small red from GPS and all other electronics will go to the "Feed" on the switch.
--- note here, you may have a single wire from the front of the boat going to some type of fuse box, add that to the positive.

Big Black from motor. put that on either negative post.
You should have another big black, going between both battery's negatives. (you may have to buy this, or already have this)
Small black from GPS and all other electronics will go to one of the batteries negative terminal.

That should be your basic setup, without the isolator. You should be able to start your boat, and run all electronics with the switch in position 1, 2 or both.


To add the isolator, add a small Red wire from your "Feed" to the common post on your isolator. Add 2 small red wires from your isolator output posts (likely the outside 2) to each battery (i.e. one on left goes to bat1, one on right to bat 2)

That should give you what you want

Some conveniences you may want to consider.
Electricity does not really care which side of the wire you connect (if they are short), so you can use this to your advantage to simplify your battery connections.

You may find it easier to connect the output posts of the isolator to your switch. put them on the input side (marked 1 & 2, or A & B). You have it drawn this way in your diagram. Don't go through the isolator and "feed back to the switch" because that is your starting circuit (i.e. the most power) keep that as simple a circuit as possible. battery to switch to motor is best.

You may find it easier to connect all the grounds to a common "bolt" and have 2 wires(Big ones) going from the bolt to the negatives on the batteries. you don't have it drawn this way.


Note: use at least a 10gauge wire to and from your isolator. when I say Big ones, this should likely be 2 gauge or less (lower numbers = larger wire)

Also. I really like to have at most 2 wires connected to my battery, USGC allows for 4 I believe, but you really start to get bad connections if you have more than 1 or 2. I can get a much better connection using a bolt, or a distribution panel than I can cranking down on my battery. The added benefit, it is easier to remember next spring how to re-install your batteries.

Hope that helps. I have hacked up your diagram a little. hope it helps.

Re: Wiring a switch and isolator

Thanks Flargin- you guys are very helpful for a guy like me. ( I know enough to get me in trouble! and then you get me out of it)

As for your suggestions, it will be easyI just need to
to add a 1' piece of wire and move the motor + red to the feed... I already have the positives for both batteries to the peg for their respective switches and tied from there to the isolator.

I also have a 7 inch jumper bar connecting the 2 negatives of the batteries then going to the black - line of the motor.

I think this should knock out this project.... now on to prop hunting!

Re: Wiring a switch and isolator

Why do you have an isolator when you have a switch. Why not just one or the other.

Re: Wiring a switch and isolator

correct me if I am wrong, but if I have a justa switch, then I am charging what ever battery the switch is on(1, 2 or both) I just bought a new battery which will be my primary, with the old battery as a back up, I want them independent of each other, unless absolutely needed.

Now I can run my primary battery independantly, while charging the back up and not letting it just sit and discharge.

Re: Wiring a switch and isolator

Set the switch to BOTH and both will charge. Seems to me you are making this way more complicated than it needs to be. With a switch, when you get where you are going and don't want to run down the start battery, switch to the house battery. Done deal and a lot less wiring. Just look at the points of failure you are adding to this system. Yikes!