The key grounds the CDI, when you turn it to the on position. Your key switch probably took a crap. Either that, or one of the two wires has a break in it somewhere. To diagnose the key switch, unplug it. Make a jumper wire. The bike will not run, with the switch unplugged. Now, take your jumper wire, and jump it across the two terminals that have the Black/Red Stripe wire, and the Black/White Stripe wire. Now, crank up the motor. With the engine running, take the jumper wire out. That should kill the bike. If that works, your key switch is bad.