Re: Cig lighter kill switch

[Norman Boehl <nboehl@xxxxxxxxxxxxxxxx>]

I posted the original message regarding the cigarette lighter, and have
implemented it on a General Motors vehicle (sorry, guys).  It works
great (the kill switch is completely out in the open and easily accessible,
but who would suspect? (probably thieves :^()).

First of all, the cigarette lighter is in itself simply a resistor that acts
like a switch whwn it is pushed in.  It "switches" +12V through itself,
and the current heats the lighter element.  When a certain temp is
reached, the switch opens up...  Ok, enough for how a lighter works!

The lighter is connected to +12V and ground.  If you disconnect the
two wires from the lighter, all you have left is a simple switch (with
a small amount of internal resistance (about 1 or 2 ohms)).

The idea is to use a relay (normally open type) and the lighter
(acting as a switch) to control the "start" signal, exactly in the same
manner as any other "kill" switch.

1) Find the "start" signal in your BMW (its accessible at the diagnostic
    connector, ignition switch, coldstart valve, etc.), and decide upon a
    suitable point at which to cut the wire.

2) Cut the "start" signal, and wire the two ends to the output of the relay.

3) Disconnect the two wires from the cigarrette lighter socket.

4) Connect one terminal of the cigarette lighter socket to one of the two
     input terminals of the relay.

5) The other cigarette lighter terminal MUST be connected to a +12V source
     that is active when the ignition switch is turned to the "start" position.  If
     not, the relay will not close when the ignition key is turned to start, and it
     will never start.

     You can actually use the hot side of the cut "start" wire to power the relay
     itself.  If so, once the car is started and running, the relay has no power
     going to it (remember, it only needs to be activated during the starting cycle).

6) Do not be concerned about the low resistance of the cigarette lighter/switch.  This
    resistance compared to that of the input terminals of the relay is very small, and
    so the voltage drop is minimal.  The relay input terminals provide a high
    resistance, and so the current flow is kept very small.

This is exactly what I did to my vehicle, and it works great.  I simply unplug the
lighter when I leave the car, and push it back in when I want to start it.

Norm


Sanders, Ron wrote:

> Someone mentioned turning the cigarette lighter into a kill switch.  A
> literal example of how smoking kills!  For those of us who barely know how
> to change a headlamp, could someone post details on how this kill switch is
> done?
>
> Ron Sanders
> Phone: 404-639-4678
> Fax:      404-639-2980
> Email: RLS5@domain.elided

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