Starter kill switch-Anti-theft scheme

[Tom Dunlap]

After thieves cut off my catalytic converter in December I've been thinking about car theft. I never let my vehicles idle unless I'm right there and the doors get locked if they are out of sight in public.

There are easy ways to wire in an Open/Closed kill switch into the fuel pump or starter circuitry. Nothing complicated, it just requires being clever when you hide the switch and wires.

But, the driver needs to remember to switch it Closed after stopping. Years ago I installed door switches for an alarm system. I forgot to arm the system and someone busted the wing then ripped out the stereo. Ooops!

I'm wondering if there is a way to wire in a spring loaded switch that automatically resets itself.

Here's my idea of how I would want it to work.

Driver puts keys in ignition
Flips the switch to Closed
Start engine with key
Drive like normal
Park and pull key

The spring loaded switch would arm itself without having to be manually flipped Closed.
It would be powered or killed by a closed circuit once the engine is running.

Does this make sense? I'm having a hard time explaining the automated part.

I'm not real clear about how relays work but my thin grasp of their function tells me that this is an application for a relay combined with a spring loaded switch.

There's an auto security shop not too far away I'll see if they can shed some light on this too.

Something that surprised me over and over about the people who come to Treebuzz is the varied knowledge base that's represented. The subject matter of trees is one thing...but then I read what else people know...wow! My guess is that there is an electrical tech reading that knows what I mean.

 

[Jehinten]

I wouldn't consider myself an electrical tech, but I did electrical work for about 5 years and I often over engineer things just for fun.

What your wanting sounds doable with a relay and a monetary switch, all it needs is a control power (any random power circuit) that when you press the button it closes the circuit for the fuel/ignition. Just check the function on your relay before installing it to ensure it will hold the circuit closed after the monetary switch is released, until the voltage is shutoff (key turns off and resets it)

A similar all inclusive switch would be like a Murphy switch, on equipment a Murphy switch requires special gauges to monitor and shutdown the engine if there is a problem. Without the correct gauges, the Murphy will not shut down the engine but it will still require the switch to be pressed while starting.

A word of caution however, if you add something like this, it'd be easy to forget to check it in the event that your car won't start. Leading you on a while goose chase of mechanical problems, where all of the symptoms are saying your fuel pump is bad (assuming you tie into the pump) when in reality it's your switch or relay.

 

[Tom Dunlap]

@Jehinten

thanks for the insights

The idea came to mind after watching a You tube vid about wiring the horn into the switch. Interesting but I don’t care to have the horn go off every time I start the vehicle. The switch interrupted power from the starter That’s fine but the thief could grind on the starter I’d rather have it wired so it’s dead unless switched on

Having it automatically reset is my idea of a better setup

onto the next step

thanks

 

[Porqchop]

I was thinking the same thing at first (I think)... Use a relay held closed by key on power, I was even thinking momentary switch to override it, but then I realized when you turn the key you turn on that circuit so the override is unnecessary, and if you hot wire the vehicle, you energize that circuit anyway... So not going to do what we want.

Also, having the fuel cut could be good because the theif wouldn't necessarily know the cause of no-start, but they could do some damage cranking the engine for a long time trying.

You could use a momentary switch and relay (you just need one switch, but the pair makes it easier to wire and not drag power into the cab and back out) to interrupt the circuit to the trigger side of the starter relay so no crank unless you push the button and turn the key. Or could be a toggle so you just turn it off when you want to disable, but you said you wanted automatic fool proof.

You could also put that switch in the wire at the ignition switch, and keep it all at the dash level. Could cut power coming into the ignition switch so everything is dead.

I think with security, it's not a matter of making things impossible, but making it obscure oe difficult enough that your theif won't persevere. So a random switch could be obvious enough to you, but they don't know what you know, so when they key doesn't work normally, they move on.

Sent from my Pixel 3 using Tapatalk

 

[Cereal_Killer]

If you go the starter kill route you don't need an on-off "latching" switch that you have to remember to flip off each time, you can just use a momentary push button. Hold down while starting and that's that. The starter wire can be disconnected and the engine keeps running.

Thinking more, the ignition circuit of your vehicle likely has a wire that's only hot while the engine is actually running, you could use this wire along with a momentary button to feed a relay that interrupts the fuel pump circuit. Cut factory wire to FP, add in interrupt circuit, push hidden button to energize relay during starting then the hot-only-when-running wire from ignition would hold relay on till you shut the vehicle down.
It'll take more investigation to find that circuit but it'd provide slightly more security than just the starter kill.

 

[Evan Sussman]

This is the same type of circuit as I've thought of making to temporarily disable a reverse alarm. We purchased a used ambulance and it has a momentary switch that does this. Every time you click it into reverse the alarm normally activates. If you click the switch is disables the alarm for that cycle. If you switch to drive and back to reverse it activates again.

It takes some special use of a relay. I found a guide on it once.

 

[Evan Sussman]

Here's a guide for that. I know it's not quite the same, but electrically it's very similar.

A Vehicle Back Up Alarm With a Self-Resetting Disable Button

A Vehicle Back Up Alarm With a Self-Resetting Disable Button: At one point I was in charge of maintaining the safety of a fleet of large, unwieldy vehicles. I thought that putting back up alarms on the trucks would increase everyone's safety during maneuvering in the parking lot, but I hated...

www.instructables.com