A friend of mine has a 1998 ZL 500 He wired an after market kill switch and tether cord in to it and it ran fine. Last weekend he was riding it and it fell on its face and started running really bad and now you can start it and it will run fine but nothing will shut it off except for pulling the plug wires. He checked all the wiring and tried one switch at a time and still no luck, nothing will shut it off. Could it be the CDI Box? If not what do you think it could be? Thank you for you help.

This is usually cause by antifreeze getting in the connections between the cdi and stator. Try cleaning, drying connections and then put dielectric grease in connectors to help keep moistier out.