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Kill Switch Wiring

Discussion in 'Technical Q&A' started by pma1010, Feb 20, 2004.

  1. pma1010

    pma1010 F1 Rookie

    Jul 21, 2002
    2,559
    Chicago
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    Philip
    Has anyone done this on a 308 and provide guidance?

    I have an OMP (dual pole). Wiring diagram shows to put this in series with the positive battery terminal and the main electrical feed (which means I can use the supply to the AMP module in the 308) with separate interrupt for the alternator (to ground it after the switch is triggered).

    To ground the alternator, it looks like you need to run wiring to interrupt the feed wire from the starter motor (which comes straight from +ve terminal on the battery) to the alternator and have another contact go to ground through the (supplied) resistor. Schematic attached.

    The problem with this is both accessing the alternator wiring (which is something of a challenge) and the need to run pretty good sized cables from the engine to the switch (which will be located in the cockpit) and they'll likely run alongside the coolant pipes through the "tunnel" under the car.

    Anyone advise a "better" solution?
    Philip
     
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  3. rexrcr

    rexrcr Formula 3

    Nov 27, 2002
    1,572
    Kalamazoo, MI
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    Rob Schermerhorn
    Consider running remote cables to actuate switch. Then you can install the switch in the engine compartment. This is what we all did in Challenge, and I've done it on other cars since. A cable running in a Teflon sheath, like a mechanically actuated fire system. May ease wiring complications.

    Rob
     
  4. Steve Magnusson

    Steve Magnusson F1 World Champ
    Lifetime Rossa

    Jan 11, 2001
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    Steve Magnusson
    Can you guys please give some background -- what is it that you're trying to accomplish that couldn't be done by opening the +12V to the ignition system on a '77 308?

    Are you trying to have a way to remove all +12V power in the whole electrical system?
     
  5. pma1010

    pma1010 F1 Rookie

    Jul 21, 2002
    2,559
    Chicago
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    Philip
    Steve
    I've put in fire suppression system for track use. The issue is the need to kill all power before pushing the deploy button, otherwise a fire can just start again and now the halon's shot. The ignition switch doesn't do this -- there's a set of non-switched ancilliaries that still get power. Just taking the battery out of the circuit doesn't do it either for the period of time when the power's cut and the alternator is still turning (3 seconds or so). Hence the need to interrupt battery supply and ground the alternator.

    Rob,
    Good thought. The other location I've heard about is putting the switch up near the headlight area with two cable tugs, one into the cockpit through the firewall and the other up to the base of the windscreen under the bonnet [hood]. Was the challenge car wiring as I describe?
    Philip
     
  6. Steve Magnusson

    Steve Magnusson F1 World Champ
    Lifetime Rossa

    Jan 11, 2001
    19,360
    Texas
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    Steve Magnusson
    Grazie -- understood.
     
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  8. pma1010

    pma1010 F1 Rookie

    Jul 21, 2002
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    Philip
    Rob
    Have a pic or any advice on where in the engine bay you'd locate the switch? Also, where did you source teflon sheathed cable?
    Thanks
    Philip
     
  9. rexrcr

    rexrcr Formula 3

    Nov 27, 2002
    1,572
    Kalamazoo, MI
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    Rob Schermerhorn
    Sourced from Ferrari. Part of the Challenge parts catalog. I don't remember cost.

    Actually, on 348, Ferrari had ECU feedback concerns, and had us performing some re-routing, and I no longer have that schematic. Your wiring schematic is sound: cut main 12V+, then drain alternator output to ground via big watt resistor.

    Aircraft control cables will work, as well as throttle cable from race supply places. I guess it's possible an auto supply like NAPA may have something, but typically, it's just manual choke cable in metal sheath, which is not what you want. A manual cable release from a fire system will do, too.

    I'd put the switch where the wiring is most convenient, and routing remote releases was straightest. For 308, I put one near the cowl, but this was an all-out racer, not a beautiful road car like you have.

    Carry a spare key for the switch, I've broken them in the past.

    Rob
     
  10. jselevan

    jselevan Formula 3
    Rossa Subscribed

    Nov 2, 2003
    1,854
    Philip - If you ground the field source from the voltage regulator, your alternator will stop generating current. Thus, at the time that you open the battery you grounded the Field wire going to the alternator AT THE REGULATOR, you have effectively taken the alternator out of the picture. This would allow you to do your dirty work at the voltage regulator rather than digging in the engine bay. (This assumes that the regulator is not built in to the alternator - which many are). The output of the regulator typically has an internal bias resistor to ground, thereby protecting the output from a short to ground.

    Jim S.
     

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