Battery cut off switch

Mopar Racers Forum

  1. 66dartman

    66dartman Well-Known Member

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    What is the best way to kill the engine with the battery cut off switch for tech? The alt keeps the engine running, so should I use a relay to interrupt the field wire? Or the msd ground wire? I've been fudging this at tech every year but I want to fix it right.
    Thanks in advance.
     
  2. 67Dart273

    67Dart273 Well-Known Member

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    First thing we need to know is how is it wired now. Do you have only one big cable going up front?



    It would be a heck of a lot easier if you would buy a 4 terminal switch
     
  3. 69Post

    69Post Well-Known Member

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    Or run the alt output to the battery side of the battery cutoff switch.
    John
     
  4. mjs69gts

    mjs69gts Well-Known Member

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    get a 4 pole cutoff switch
     
  5. 66dartman

    66dartman Well-Known Member

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    Thanks, maybe the 4 pole switch is the way to go.
     
  6. TAZLDAZL

    TAZLDAZL AMSOIL DEALER

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    Hey Dartman,
    I'm in the process of rewiring my Demon/racecar and I too had the two post cutoff switch and it wouldn't shutoff the car. I was shown the 4 post alt/battery cutoff switch. I will be using this in my setup now. Was told that this would take care of the same situation you have.
    Good luck
    TAZZ

    http://static.speedwaymotors.com/RS/SR/Product/91064501_R.jpg
     
  7. 67Dart273

    67Dart273 Well-Known Member

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    Here's one easy way to do it:

    Buy one more good heavy relay or "continuous duty solenoid." These have two coil terminals, not grounded to the case. Run one small terminal to "ignition run." Run the other to the rear with no14 or 12, wire it to ground through the small terminals of the disconnect.

    Hook one big stud of the continuous duty sol to the batt. term. of the starter relay, hook the other either to alternator field or the ignition system/ regulator feed. I did not show a fuse or breaker in that circuit, a good idea. If you feed the output of the solenoid to the "blue" ignition run, it will control BOTH ignition power and alternator field on 70/ later isolated field units, as well as the "input" of the regulator.

    Run your starter cable to either the starter, the relay, or a big junction stud and interconnect as shown.

    [​IMG]
     
  8. 66dartman

    66dartman Well-Known Member

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    Thanks 67Dart273, looks like something that will work.
     
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    • Timmy's Toy

      Timmy's Toy Well-Known Member

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      Is it my imagination or is the scenario drawn up by 67Dart273 a little convoluted? I ran a #8 wire from the alt ouput stud to the battery side of the switch just like 69post said to do and it works awesome. Very simple and effective. Why all the additional wires and relays? Is there something I don't understand here?

      Tim
       
    • briankaplan

      briankaplan greenduster

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      I had the same problem. I just ran the alt to the battery side of switch
      also.
       
    • AtomicWedgie

      AtomicWedgie Well-Known Member

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      No need for all that extra stuff.

      X3 on the 8ga. wire to the Battery side of the cut off switch.

      Take the "power" wire that runs from the alt to the bulkhead and throw it out. Now run a new 8 ga. power wire from the Alt. to the battery side(OFF) of the cut off switch. IT WILL CUT THE CAR OFF. If you run the wire to the (ON) side of the switch then it wont shut the car down. I have never failed tech with mine hooked up this way.

      Not saying the other ways don't work but not sure why would you go through all that wiring to do the same thing.
       
    • Timmy's Toy

      Timmy's Toy Well-Known Member

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      I believe that's what I said to do. All I have is just the 8ga wire from the alt to the battery side of the cut-off switch. Turns the car off every time and continues to charge the battery. Simple!! and cheaper too!
       
    • 67Dart273

      67Dart273 Well-Known Member

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      I don't believe the diagram is convoluted, nor are there a "bunch of relays."

      TWO wires front to rear, and ONE relay/ solenoid up front.

      You can use the relay up front to break the ignition path to the "what was" "dark blue" lead, that is, break the "ignition run" use the wire from the ign switch to power the relay, run the other half that fed the igntion, regulator, and alternator field to the relay contacts. This way, EITHER the ignition switch or the battery kill switch will kill the ignition. If you later go to a "one wire" alternator, you will be all set up.

      Here's the deal: If you run a no8 cable from the battery to the alternator, YOU DO NOT HAVE a disconnect. What you DO have----is a large hot wire from the battery to the front of the car, hooked to the alternator!!! Some of the other diagrams floating around also show a second or even third solenoid.

      If you leave the no8 run up front "hot" I don't believe it will meet the letter of the NHRA rules
       
    • crackedback

      crackedback FABO Gold Member FABO Gold Member

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      The relays are to kill all the power to the front.

      The NHRA only cares that the master switch kills the engine/fuel pumps.

      If you've never had a car or seen a car burn to the ground because of that always hot alt wire, then you may not get why some of us use an extra relay. On my cars, you throw the master, NOTHING and I mean NOTHING is hot outside a 2' cube in the trunk PERIOD!

      Crude diagram with a S605 relay in the alt charge line but kills the system flat!
      [​IMG]

      If you have a street car, the switched/activation lead wire for the S605 needs to come from a keyed source, otherwise, when the master switch is on, there is a constant draw on your battery the way the diagram shows. Not hard to accomplish.

      I also don't like a 0 gauge or larger wire being hot all the time either, thus the ford relay. Yeah it takes a bit more wire, rather have a smaller gauge wire short than a 0 gauge or larger.

      There's a minimum acceptable NHRA standard and there are improvements, I prefer the latter.
       
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      • Oldmanmopar

        Oldmanmopar Going left turning right FABO Gold Member

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        One wire alternator. Cut the power kills everything. I have a 100amp GM alternater . But my friend has a chrysler alternator converted to a one wire. No extra wires relays or solinoids. Just one wire coming from any power source thats interupted by the disconnect. Doesn't get any simpler. My battery cable coming from the trunk goes to a single stud bulkhead post on the frame next to the motor. That acts as my pos. battery post under the hood. From there I ran a 7 Inch wire to the alternator and that is all you need .
         
      • Oldmanmopar

        Oldmanmopar Going left turning right FABO Gold Member

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        posted twice
         
      • AtomicWedgie

        AtomicWedgie Well-Known Member

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        CRACKEDBACK: I get what you are saying so if i was going to change my "simple way" over to your "complete" way.

        Do I just follow it as drawn or do I need to change anything since I don't have a 1 wire Alt.


        I have done the "EASY" way for years and on alot of cars. I have never had a problem but I am open to new and improved ways. I do like the idea that when it is cut then it is 100% dead.
         
      • 67Dart273

        67Dart273 Well-Known Member

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        This cannot work, and if you don't believe me, try it

        Start the engine, bring RPM up enough that the alternator is for certain charging, and then have a buddy go back and yank the disconnect. You will find that the engine keeps right on running
         
      • 67Dart273

        67Dart273 Well-Known Member

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        I've said it before, the thing I don't like about crackedback's diagram is that anytime the battery switch is on, so is one solenoid. This may not be a big deal on a race-only car, but to me, it's a big deal on a street car. I don't want to park my car for a day, and come back and find the battery dead because I happened to leave the switch on. Also, those solenoids DO occasionally fail, so it would be a good idea to fuse the control wiring.
         
      • Timmy's Toy

        Timmy's Toy Well-Known Member

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        Okay, the "am I missing something" question that I had has been answered by 67dart273 and crackedback. However here is what I know about NHRA. They do not care about the power being hot up front. What they are concerned with is that when the switch is shut off everything stops. The engine, the fuel pump, fan motors, everything. The simple way does make that happen. Now I will concide that if there is power still to the front at the alternator that it could be an issue for an electrical fire. But I've spoke with 3 different NHRA saftey inspectors and the "simple" way as described in these threads meets the NHRA requirements. But I do agree that the relay system as described by 67dart273 and crackedback would be better safety wise and for street driven vehicles. Thank you guys for the clarification.
         
      • 67Dart273

        67Dart273 Well-Known Member

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        Here's how I look at it

        You guys might ask yourself "do I just want to squeek by the rules" or "am I really doing this for safety?

        So you're layin' there on the ground half dazed, wonderin' why the steering wheel doesn't look right, and the road to ruin is layin' on the roof.

        Somebody comes along and kills the battery, BUT YOU STILL HAVE a live no8 or 6 running up front to the alternator.

        I for one would prefer that ALL of it is dead, and that leaking gas, oil, is not gonna light off because the alternator has a short "up there"

        It's only one relay. It's only one no14 to the rear. It's only a couple of changes to the wiring up front.

        You guys in better shape than me should be able to install that relay in a couple of hours easy, and drink a beer or two on the way.
         
      • tgee43

        tgee43 New Member

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        Am going to run a chrysler 2 field wire alternator. I am going to run a 14 gauge wire between my single pole disconnect switch to one field terminal at alt. Kill the field, kills the alt, thus kills all juice.
         
      • 68 HEMI GTS

        68 HEMI GTS Well-Known Member

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        thats how i did mine, works good
         
      • Oldmanmopar

        Oldmanmopar Going left turning right FABO Gold Member

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        After going out and looking at my car you are right. I have a 4 post wired in. I am killing the ignition box and the fuel pump with the smaller post.
         
      • SlimPikins

        SlimPikins Pikins, Slim Pikins.

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        That's the way I just wired mine. 4 post switch. I ran a 8 gauge wire from the small post to my msd box. Flip the switch and it kills the power from the battery, and the power to the ignition. When off, there is no power in the car. No relays needed.
         
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