Battery Shut Off Switch

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I use on on the negative cable. If you are racing, you need to see the specs.
I use it on the negative cable to shut off the power when the car is not going to be used in a week or so. I have a trunk mounted battery and the switch is mounted by the cable with the lever under the car. Even with my other projects I unhook the neg. cable.

Battery Switch.jpg
 
Negative side. No spark to damage contacts if under load.

think of it this way- jump starting a car from another. Ground is always connected last because if it falls off it does not spark. Disconnect the positive and you get sparks.
Same thing is going on inside the switch contacts.
 
Syleng1 said:
Negative side. No spark to damage contacts if under load.

think of it this way- jump starting a car from another. Ground is always connected last because if it falls off it does not spark. Disconnect the positive and you get sparks.
Same thing is going on inside the switch contacts.
Click to expand...

LOLOL Sorry man this is NOT TRUE. If you are switching something "hot" drawing CURRENT under LOAD it does not matter where in the line the switch is placed. The switch will still "eat" the contacts

Your reasoning has to do with if you SHORT something to ground then it sparks When connecting jumpers, you want to connect the ground last, BUT AWAY FROM THE BATTERY such as at the engine block. IT WILL SPARK if the jumper is hot and the target is low. The reason you want to connect away from the battery is THAT SPARK when connected will not trigger a possible battery explosion.......and it happens
 
NHRA requires positive, and you must take steps so that the alternator does not keep the engine running. So if racing you need a 4 post switch, properly called DPST which means "double pole single throw."

I agree with the others, if you don't go to the track just put it in the ground lead
 
67Dart273 said:
LOLOL Sorry man this is NOT TRUE. If you are switching something "hot" drawing CURRENT under LOAD it does not matter where in the line the switch is placed. The switch will still "eat" the contacts

Your reasoning has to do with if you SHORT something to ground then it sparks When connecting jumpers, you want to connect the ground last, BUT AWAY FROM THE BATTERY such as at the engine block. IT WILL SPARK if the jumper is hot and the target is low. The reason you want to connect away from the battery is THAT SPARK when connected will not trigger a possible battery explosion.......and it happens
Click to expand...

I stand corrected. I also like the idea of a positive shut off because if a ground - well shorts to ground- no issues.
If a positive grounds- big issues. Thanks for the street version of edumacation en me!
 
You don't need a 4 post switch.

If going NHRA legal it must be on the positive cable. There are many ways to do it, some are legal but not the safest. If you want minimum the main cable runs through the cut off and heads to starter. Alternator wire runs to back of car and attaches on battery side of switch. The OEM black wire must be disconnected at alternator. Run a jumper from starter lug to starter relay 5/16 stud. I do not like this method, but it is legal and gets by. Not a fan of the always hot alternator line.

This is legal, ackkkk

trunkbattwire2.jpg
 
On my first trunk mounted battery project I switched the negative. Not a race car and seemed the easiest. On my new project (also not a race car) I plan to switch the positive because I want to use the switch as a theft deterrent on occasion but keep juice flowing to an alarm (and maybe the radio to save presets). The switch will be for the big wire but I'll keep the alarm and/or radio hot all the time with a fused, non-switched wire.
 
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