If its a 2 stroke the you can put it inline with the positive magneto wire. If its a four stroke its a tad bit more complicated. I had a thread on it a while back. You need to wire up the kill switch with a relay so that when the key is out the relay is closed and completing the kill circuit and when it is turned on it opens the circuit. I used a 12 volt car relay with a 9 volt battery. Never had to replace the battery in about 7 months maybe more. I have a wiring diagram for the four stroke if needed.