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Old 10-11-2017, 10:47 PM   #1
REByar
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Default Battery disconnect switch- on positive or negative

I purchased my 1928 Tudor 5 years ago. At the time the previous owner had the disconnect switch on the positive post of the battery. The cable then went to the frame. The negative is directly connected to the starter. It has been fine. But I have recently read that the disconnect switch should be on the negative side. Does it make a difference?

Thanks for your advice.

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Old 10-11-2017, 10:59 PM   #2
Magicbox51
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Default Re: Battery disconnect switch- on positive or negative

Electrically, I don't think it matters much. The question of which side to switch might matter more if the switch is located under the seat or floorboard or in the engine compartment near the starter. Mine is in the engine compartment near the starter so it is a more natural fit to do the negative side. Negative is also considered to be the "hot" side so that is kind of what I would consider preferable. However, if the switch is such that wiring it is more conducive for a switched positive, you kind of have to wire it where the cables fit and are not excessively long, and where they can be "dressed" nicely.
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Old 10-11-2017, 11:25 PM   #3
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Default Re: Battery disconnect switch- on positive or negative

My battery disconnect switch is attached to the battery under the floor board.

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Old 10-11-2017, 11:47 PM   #4
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Default Re: Battery disconnect switch- on positive or negative

it does not matters which side you put the disconnect on. I like it on the positive side that ground to the frame, if you are running more wires to the switch, if they short out it is no big deal. on the other side if it shorts out it is a BIG deal.
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Old 10-12-2017, 12:04 AM   #5
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Default Re: Battery disconnect switch- on positive or negative

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Originally Posted by REByar View Post
My battery disconnect switch is attached to the battery under the floor board.

REB
Then it is probably wired the better of the two ways. I would leave it as is.
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Old 10-12-2017, 12:32 AM   #6
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Default Re: Battery disconnect switch- on positive or negative

I put the disconnect on the ground cable. Does not matter if it is positive or negative ground, I just choose the ground cable. Why? I retired from working on construction equipment. Some of that equipment is big and very expensive. Every brand I worked on had the disconnect on the ground cable. Some even had a solenoid disconnect where if you turned the key off, it disconnected the ground cable. I figure they should know the best way.
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Old 10-12-2017, 12:59 AM   #7
Tom Wesenberg
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Default Re: Battery disconnect switch- on positive or negative

Yes, the ground side is the best side.
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Old 10-12-2017, 08:07 AM   #8
SeaSlugs
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Default Re: Battery disconnect switch- on positive or negative

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Originally Posted by jw hash View Post
it does not matters which side you put the disconnect on. I like it on the positive side that ground to the frame, if you are running more wires to the switch, if they short out it is no big deal. on the other side if it shorts out it is a BIG deal.
Yup - same logic behind when your removing a battery - start at the ground terminal and end with the ground terminal.
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Old 10-12-2017, 10:26 AM   #9
Bob Bidonde
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Default Re: Battery disconnect switch- on positive or negative

The switch is easier to install into the battery's output cable to the starter.
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File Type: jpg Battery Disconnect Switch (1).jpg (55.5 KB, 74 views)
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Old 10-12-2017, 08:29 PM   #10
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Default Re: Battery disconnect switch- on positive or negative

Always place a battery disconnect on the ground side regardless of polarity of the vehicle. ie for a positive ground or earth, put the switch on the positive cable. Also, when disconnecting a battery always disconnect the ground/earth first. This is because the whole frame/chassis/body of the vehicle is the ground or earth of the whole vehicle, and by disconnecting the ground you avoid shorting out tools etc while working on the system or moving the battery in and out.
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Old 10-13-2017, 02:52 PM   #11
Tom F OHIO
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Default Re: Battery disconnect switch- on positive or negative

Where is the best place to mount this switch where you could get to it easy? Does anybody ever mount it in the floor board somewhere where you can reach down and shut it off while in the car.
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Old 10-13-2017, 03:31 PM   #12
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Default Re: Battery disconnect switch- on positive or negative

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Originally Posted by Tom F OHIO View Post
Where is the best place to mount this switch where you could get to it easy? Does anybody ever mount it in the floor board somewhere where you can reach down and shut it off while in the car.
thats where most ive seen are mounted - or seat riser depending on model.
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