I'm not sure if you can hook up a prodesign kill switch to a cannondale.
My dealer told me that you need a kill switch that completes the circiut when the button is engaged.
I put one from an Arctic Cat Snowmobile on mine and it was easy. You just follow the GREEN wire down to the connection, pull it apart and plug the kill switch into the wires.

I also heard that PWCs like Sea Doo or, Jet Ski use this same type of kill switch.

Hope this helps.