KILL SWITCHES: Kill switches are a fairly easy and effective way to keep your car parked where you left it. They may not prevent people from breaking into your car (that's what alarms are for) but if they do, it can keep a theif from stealing the whole car. But if a real/pro theif wants your car, it really doesn't matter what you have. They can get it.

I won't go into where you can hide a switch so as to not give away my own secret switches. But, I will tell you that it's a good idea to make the switch out of visible site, but fairly easy to access so it's not a pain to turn on and off. If it gets to be a pain to switch it then you are more likely to not turn it on and protect your car. It's simple pyschology.

Basically you want to tap into a wire source that interrupts power to a vital component like the starter or ignition. This way, even if they do get into your car it will be even more difficult and time consuming to try to take your car. And if it takes too long it becomes more riskier for the theif to stay with your car.

Using a simple on/off toggle switch will be fine. But make sure the ampage of the switch and gauge of the wire is compatible with the wiring you tap into to. This will ensure that everything works fine and won;t burn or blow anything out.

Soldering the wires is also a good thing to do. It ensures that there is a proper and solid connection between the electrical switch and wiring. Also use shrink tubes to cover the exposed wires and connectors to keep the wires from corroding.