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Old 05-21-2017, 02:31 PM   #1
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Battery shutoff switch with 2 negatives?

My battery setup has 2 negatives and 1 positive. It looks like one of the negatives goes towards the engine, while the extra negative and positive goes towards the bus. The batteries are hooked up in parallel. I want to add a kill switch so the batteries can last while sitting. Any advice on switches (like brand?) And which negative I should attach it to?
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Old 05-21-2017, 02:41 PM   #2
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Originally Posted by Iheartbus View Post
My battery setup has 2 negatives and 1 positive. It looks like one of the negatives goes towards the engine, while the extra negative and positive goes towards the bus. The batteries are hooked up in parallel. I want to add a kill switch so the batteries can last while sitting. Any advice on switches (like brand?) And which negative I should attach it to?
I am pretty sure a battery isolator just interrupts the positive. So the grounds shouldn't be an issue.

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Old 05-21-2017, 02:47 PM   #3
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Originally Posted by Njsurf73 View Post
I am pretty sure a battery isolator just interrupts the positive. So the grounds shouldn't be an issue.

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Even though it attaches to the negative? Hmm, alrighty. I suppose I can put the switch on one or the other and test.
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Old 05-21-2017, 02:55 PM   #4
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If you attached the switch with one terminal on the positive side of the battery and one on the negative, you would short the battery.
I had one in my boat. It was positive from the battery on one post and a positive lead to the starter and acc solenoids off the other leg.

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Old 05-21-2017, 03:03 PM   #5
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Originally Posted by Njsurf73 View Post
If you attached the switch with one terminal on the positive side of the battery and one on the negative, you would short the battery.
I had one in my boat. It was positive from the battery on one post and a positive lead to the starter and acc solenoids off the other leg.

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The instructions say to connect the switch to your ground (neg) it doesn't say to connect the positive.
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Old 05-21-2017, 03:11 PM   #6
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1 ground lead probably goes to the frame and the other to the engine. On the positive lead it cuts all power.

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Old 05-21-2017, 03:13 PM   #7
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I installed mine to switch the negative cable. I would pick the engine for ground to use.
I have no issues with battery drain.
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Old 05-21-2017, 04:27 PM   #8
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The race car guys switch the positive mainly to de-energise a crashed car and often switch both the battery and the alternator to keep a high revving alt from blowing up the battery with a disconnected ground. The rest of us who just want a battery disconnect usually switch the negative.

When working on a battery the conventional wisdom is to disconnect the negative first to avoid possible sparking.
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Old 05-21-2017, 04:45 PM   #9
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Most switches will be a live disconnect on the positive. You don't need a fuse or breaker for this type of application and just a switch that disconnects the circuit, so you don't have to worry about amp or voltage ratings. Maybe someone else can chime in on that because I'm not an electrician. If you have two grounds I would place the switch on the positive. That will disconnect power and avoid any drains. All of my disconnects on my solar array, for instance, are on the live feeds. I use breakers on those though. Any generic 12v disconnect switch you find on Amazon would suffice. Just make sure all your terminals are clean.
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Old 05-22-2017, 09:06 AM   #10
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The instructions probably call for installing on the ground in order to avoid having an exposed hot terminal on the backside of the switch. As long as you have a way to cover up the connections, or are just mindful to keep anything that's grounded well away from them (including tools that you're using), installing it on the positive should be fine.
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