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Thread: Battery Cut Off or Kill Switch

  1. #1
    Senior Member JOP33's Avatar
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    Battery Cut Off or Kill Switch

    Where should I install (not physically, but where in the line of wiring) a battery shut off? Keeping in mind that I need to maintain power to the bolt on Holley Sniper EFI so it doesn’t have to relearn everytime I use the shut off.

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    33' Hot Rod Coupe/Roadster (GEN 1), Fendered, Ford 302, 350hp, EFI, AOD, 4-Link, Double Adjustable Koni Coilovers, Split Rear Exhaust, Electric Power Steering, AC/Heat/Defrost, Moser 8.8"-3.55, Willwood Front/Rear Brakes, 18" x 8" Fronts/20" x 10" Rears, Ordered: 1.26.17, Arrived: 3.29.17, First Start: 7.2.18, Go Cart: 11.4.18 Paint/Body: 2.23.19, Back Home: 11.24.19, Completed: NEVER!; View More Pics @ https://starmobileone.com/

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    A battery cutoff switch usually is in series with the positive battery lead.
    Connect a wire to the + battery terminal (or where it connects to the switch) and run that new wire to your Holley Sniper EFI.

  3. #3
    Senior Member AC Bill's Avatar
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    Install the switch anywhere between the battery and the main power block, remote starter solenoid, or fuse box, if using the positive battery cable. Between the battery and wherever you ground the battery to the chassis, if using the negative cable for the kill switch.
    Jim's method will work fine for the memory.
    You could also simply run a small gauge jumper wire from one side of the kill switch posts, to the other. When the switch is turned off this "keep-alive" wire will allow the computer to retain memory. Put an easily accessible fuse, in-line on this keep-alive wire. If you ever hop in and forget to turn the kill switch back on, when you try and start it, the fuse will pop. This is preferable to that wire melting, in trying to supply the amps needed for the starter. This works regardless if using the + or the - cable to the kill switch. It still allows a completed circuit.
    Last edited by AC Bill; 12-08-2017 at 04:58 AM.

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    Senior Member JOP33's Avatar
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    Makes perfect sense guys! Thank you so much for your help.
    33' Hot Rod Coupe/Roadster (GEN 1), Fendered, Ford 302, 350hp, EFI, AOD, 4-Link, Double Adjustable Koni Coilovers, Split Rear Exhaust, Electric Power Steering, AC/Heat/Defrost, Moser 8.8"-3.55, Willwood Front/Rear Brakes, 18" x 8" Fronts/20" x 10" Rears, Ordered: 1.26.17, Arrived: 3.29.17, First Start: 7.2.18, Go Cart: 11.4.18 Paint/Body: 2.23.19, Back Home: 11.24.19, Completed: NEVER!; View More Pics @ https://starmobileone.com/

  6. #5
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    AC Bill,
    The "keep alive" fused jumper is a perfectly simple solution, thanks! I've been pondering how to keep the GPS speedo and clock powered when negative wired main switch is off. Just a 5A fuse is adequate to prevent any serious problems.

  7. #6
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    Opinions vary on where to place a kill switch. I don't have one, nor would I have any use for a remote solenoid. If the starter has it's own solenoid, then a remote should not be needed. For roadster owners, the kill switch can act as a theft deterrent, if it's a locking type.

    http://www.hotrod.com/articles/kill-...e-or-negative/

  8. #7
    Seasoned Citizen NAZ's Avatar
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    If you're going to go to the trouble to add a master switch and you're not working under some racing rule dictating how to install one then you probably should consider placing it where you can reach it when in the driver's seat. And it won't really matter if it's on the negative or positive side -- disconnecting either will stop the flow of electrons. However, if I was going to use one for a street only car I'd place it on the negative side (which is what NHRA should allow).

    Mine is mounted on the rear of the car and connected to the positive terminal as required by NHRA rules. Sanctioning bodies that regulate the location of these are more interested in track workers accessing the master switch not the driver. But I also have a way to cut power while belted in the car as I figure if that's needed I'm going to be the first one to the scene of the crash.

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  10. #8

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    I recommend you google "installing a kill switch with alternator" and look through the image results.

    Here's one i found quickly: https://www.pegasusautoracing.com/do...ocID=TECH00109

    If you want the option of killing power when the motor is running, you need to stop the alternator feeding the circuits and keeping everything running. I'm adding a kill switch between the seats, and also adding some remote posts to the trunk when I want to charge/jump the battery.

    Some kill switches come with alternator "support" (e.g. https://www.summitracing.com/parts/mor-74102/overview/) and other cheaper ones don't (like https://www.summitracing.com/parts/AWW-500930)
    James

    FFR33 #997 (Gen1 chassis, Gen2 body), license plate DRIVE IT says it all! build thread
    My build: 350SBC, TKO600, hardtop, no fenders/hood, 32 grill, 3 link, sway bars, 355/30r19
    Previous cars: GTD40, Cobra, tubeframe 55 Chevy, 66 Nova, 56 F100

  11. #9
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    If you run the cut-off switch on the negative side of the battery to be used mainly as a theft deterrent as Dave mentions, you wouldn't need to do anything different with the power supply running to the EFI right. It would always be powered, but if the battery shut off was in the off position the car wouldn't start because the ignition/starter wouldn't be grounded, right?
    Ryan
    33 Hot Rod
    350 SBC with TKO 500, 3 link rear

  12. #10
    Seasoned Citizen NAZ's Avatar
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    If you run the negative lead from the battery through the master switch you will not have continuity through any of your electrical system when the master switch is open. Same for the positive cable -- run it from the battery through the master switch and you will have no continuity when the switch is open. The exception is components that can back-feed current into the system (alternator or radiator fan).

    A "master switch" is intended to cut all power to the system but there are many ways to defeat this by creatively wiring it into the system.
    Last edited by NAZ; 01-09-2018 at 07:39 PM.

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