Are you looking to wire in a switch so the motor can not be started without it on or for a switch to kill the motor in case of a roll? Only ask as the locations and wire will vary for the 2. For a theft deterent switch, you'll need to interrupt the "start" wire and put a simple toggle in line to cut power from that function. That'll keep the starter from cranking over at all. For an engine kill switch, you'll need to interrupt the coil "+" lead. That'll cut power to the coil, killing the motor.
