Thread: Ignition circut security device

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Came across a discussion some time back on another board about how to rig a hidden security feature into your vehicle to disable the ignition circut to the coil or starter relay. Could be used if you're like myself & like to avoid having to use keys as well.

From the discussion I came up with a workable diagram using two relays & a flashing LED that can all be had at Radio Shack or another electronics retailer. Can be tossed together by anyone with a basic knowledge of wiring & a soldering iron.

All of the components can be mounted inside a small enclosure & put inline to disrupt the coil wire.

The way it works is this:
The magnetic reed switch is mounted somewhere on the interior where only you know it is, say under a door panel, and is actuvated by swiping a small magnet attached to your keychain over the spot.
A flashing 12V LED is mounted like an alarm flasher that is always on when the ignition circut is disabled. When the reed switch is tripped the light will go out & the circut is armed.
Under the dash can be mounted a simple push button switch that disables the circut.

Materials:
Dual pole, dual circut (DPDT) 12V relay
Single pole, single circut (SPST) 12V automotive relay
Normally on/momentary off push button switch
12V flashing LED
Reed switch, normally open
Magnet

Just a few comments, how do you turn the engine off if you don't use keys? If its hooked to the coil negative, you fry the contacts cause the coils puts out one final spike around 300 volts when turned off. Thats why old points systems used a condensor to prevent points pitting. The relay or switch should be on the B+ side of the coil. Also, a standard ignition coil draws 6 amps. The relay needs to be rated higher than 2amps. If you hit a bump or lose power to the relay does the car die if it's hooked in series with the coil? The LED needs to be currrent limited to about 10mA. Do you have a resistor in series with the led or is the 1200 ohms you need to limit the current to 10 milliamps built in? I am not knocking you, just don't want you or anyone else to have problems down the road or on the road.

Hey VW dont give up, but an old tow truck driver like me would simply hot wire your car cause there is no locking column. Now u might just want to use the stock ignition lock and run apower cut off switch or fuel shutoff.

Fuel cutoffs are great on carbs because it lets them get the thing started and maybe moving before it dies....kinda tough for them to troubleshoot after they get it out into the street.

The primary relay is held on by a ground loop thru the relay itself keeping it energized once the magnet is removed from the reed. The kill switch is inline with that ground, depressing it (momentary open) deenergizes the primary relay, & subsequently the secondary relay.

The secondary relay goes in the positive side of the ignition coil wire. Basicly it comes off the ignition fuse, into the relay, & on to the coil.
Now this same setup could be used to kill an electric fuel pump, or even do both if you wanted to run two secondary relays in paralel, one for each item.

The 12V automotive relays I have used are rated for 15-30A, they are used for items like fog lamps & driving lights, so running a coil or fuel pump is no problem & the wide contact area can handle a power spike w/o fusing.
They are very resilient to bumps/shock/etc. But yes, loss of power to the primary solenoid would kill it & of course the engine.
I've run a few different varieties of relays in my baja, & never had one fail due to bumps, so I would feel comfortable recommending this setup for cars that wont see that kind of deliberate abuse.

The 12V flasher LEDs dont need an additional resistor, they are built into the unit, all they require is power.


If someone wants it bad enough it's history, period. I just wanna make it hard for the amatuer pukes most of us have to deal with.
You can hotwire most anything with a couple lengths or wire with clips on em. How far is it from the + pole on your starter & the + side of your coil & to your ign. solenoid? Two pieces of wire & it's gone!
Enclosing the connectors & adding relays in the circuts just makes it that much harder for them to get away with your baby. The more time it takes em, the less likely they are to mess w. it.