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Old 04-14-2020, 06:02 PM   #1
Epetek1
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Default model a battery disconnect question

does it make a difference whether you use the positive or negative post to attach a disconnect. Also the usual imported ones are troublesome. I spent a few hours when my car wouldn't start before i found out that the connections are hard to tighten properly. Any hints or ideas appreciated.
Thanks Pete also best email address for me [email protected]
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Old 04-14-2020, 06:52 PM   #2
Synchro909
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Default Re: model a battery disconnect question

Not knowing whether your car is 6 volt +ve earth (ground) or 12 volt -ve earth, I will not say +ve or -ve, just active or earth side of the battery. It is best to put the cutout on the earth side - that is, between the battery and your earth connection at the chassis.
That way, when it is turned off, everything is dead and no short circuit to earth can cause a problem.
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Old 04-14-2020, 07:02 PM   #3
DBrer
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Default Re: model a battery disconnect question

I agree with Synchro909 the ground cable should have the switch in line. I mounted my switch between the front seats on my 29 Tudor. Very easy to turn the switch on or off.
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Old 04-14-2020, 10:43 PM   #4
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Default Re: model a battery disconnect question

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I agree with Synchro909 the ground cable should have the switch in line. I mounted my switch between the front seats on my 29 Tudor. Very easy to turn the switch on or off.
In my Tudor, it is mounted on the cross member between the seats. To turn it on or off, I just poke my finger through a slot in the carpet. It's nearly invisible.
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Old 04-15-2020, 05:44 AM   #5
Bruce of MN
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Default Re: model a battery disconnect question

This is where the switch is in my Coupe:

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Old 04-15-2020, 09:09 AM   #6
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Default Re: model a battery disconnect question

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If the ground cable has the disconnect switch, and something with a hot lead in the car sorts to ground, then current will flow from the battery regardless of the disconnect. In my opinion, a disconnect switch is best put into the battery cable going to the starter.
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Old 04-15-2020, 11:08 AM   #7
30 Closed Cab PU
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Default Re: model a battery disconnect question

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If the ground cable has the disconnect switch, and something with a hot lead in the car sorts to ground, then current will flow from the battery regardless of the disconnect. In my opinion, a disconnect switch is best put into the battery cable going to the starter.


Not sure I understand, if the ground battery post is disconnected by the switch, how can there be any current flow?
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Old 04-15-2020, 11:27 AM   #8
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Default Re: model a battery disconnect question

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Originally Posted by Bob Bidonde View Post
If the ground cable has the disconnect switch, and something with a hot lead in the car sorts to ground, then current will flow from the battery regardless of the disconnect. In my opinion, a disconnect switch is best put into the battery cable going to the starter.
With no ground on the battery there will be no current flow from the hot side of the battery. The vehicle frame has no continuity to the ground lug on the battery with the disconnect switch on the the ground side and the switch off (open).
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Old 04-16-2020, 08:55 AM   #9
Bob Bidonde
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Default Re: model a battery disconnect question

Good points guys. I stand corrected.
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Old 04-16-2020, 09:26 AM   #10
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Good points guys. I stand corrected.
You must have had a brain burp. I always read your posts, always informative and trustworthy.
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Old 04-18-2020, 06:20 AM   #11
mobil101
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Default Re: model a battery disconnect question

I prefer interrupting the ground side of the battery, + side, for several reasons.
It's generally easier to deal with the ground cable to chassis. Also if you
interrupt the hot side of the battery and the disconnect switch shorts to ground
you have instant full blown short. Had a couple of farm tractors do that. Thats
how i know. Always buy a heavy duty disconnect switch. Lots of Amps
flowing through that switch when starter is engaged. Lastly, when you put the disconnect on the hot side, your creating two more connection points in an
area that is prone to water and road debris (more shorts).
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