simply put, run a wire off of the ground terminal of your ignition coil to the one of the switch terminals, then run another wire from the other switch terminal and ground it out somewhere on your frame.....when you press the switch, it breaks the connection between the ground and the coil, and the motor shuts off.
it depends on your switch!!
its best to take a switch whos normally closed then you just place the switch in series with the either terminal of the spark coil coming originally from the CDI, so when the switch is pressed one direction its a short circuit and when its pressed the other its an open circuit and breaks the connection from the coil to CDI hence killing your spark
just go to a diy shop and buy a switch its easiest thing to do
actually we sell a kill switch for motorcycles, it's the "off" & "run" type, basically when it's on the "off" position the circuit is broken & when it's on "run" the circuit is connected to the ground & ignition fuctions once again.
we put our switch between the - of ignition coil & ground (earth) very easy to do.
it doesn't really depend on the switch, if the circuit is closed one way, simply revers the wires and it will be open the other Eoin70. Not really that complicated.