lol, easy, the left side should be the key side where you put in, so when u turn to start, the line goes to the right side, and connect to the "box"/switch and it will joint the current to the 12v ignition. If you turn that swith to open cct, then no matter how you start the key it wont on. It's a simply cut off electric.

What i do suggest is a most simple cutoff is, you make a switch that connect your magneto starter ground, on connect to ground, off normal. which is the person want to steal also impossible, no matter how good he is to break the key side to connect the wire,