Two Stage Kill Switch with Horn Sounder

Hi I just signed up as I am looking for a bit of advice on if my kill switch idea is feasible and the relay plans I have sketched are right. I'm wanting to run a two stage kill switch, one decoy/secondary toggle switch and a hidden momentary starter motor switch that will sound the horn when the key is turned if not deactivated. I would also have to incorporate an override for MOT's and repairs. I have a basic knowledge of electronics but would be up for giving this a try.

There's only two things (possibly a third) wrong with that implementation. The first, the Ignition ACC needs to have 12v in the start/crank position and most vehicles drop the ACC feed during cranking. Second, your override switch defeats the toggle and momentary switches thus making it the weak point in your multi-switch security. Finally Third, while this system is easy to implement on older vehicles, modern vehicles often don't have ignition switch circuits that lend themselves to kill switches like this. If this an old vehicle, this kill switch would work once you change the Ignition ACC to an Ignition RUN source. If it's a more modern vehicle, most of those have factory immobilizers to deter/slow theft and are equal to if not better than this custom kill switch. A step-up would be to get an actual aftermarket alarm that has kill switch functionality (they virtually all do) that will notify you when someone enters your vehicle and not just when they turn the key to the crank position.

It is a 2004 Corolla Tsport. The override intentionally defeats both other switches. It will be hidden in a very awkward place (such as behind the door card or underneath the centre console) somewhere that needs unscrewing and effort to reach as it would just be to allow the garage to not have to worry about kill switches. The main reason I want to install is so that I can leave the keys in the car at a show to have power running to lights and stereo without having to worry about someone jacking it. Might just be easier to install a secondary battery for those than trying to wire up a starter kill switch. I enjoy challenging myself and learning new skills so though the starter kill would be more fun.

The lower relay needs to be wired as a latch, otherwise the momentary button needs to be held during cranking. A diode between 86 and 87, band towards 86 would accomplish this.