I use my my kill button all the time!
I love it!
Granted I ride a Jackshafted 3-speed but I kill the motor all the time, like 1/2 way down the road to my house and coast up, or sitting at a light.
Provided the button is good, if you just hooked one wire to the White motor wire and the other to the frame it won't work if the motor is not also grounded to the frame.
You can just loosen one of the clutch plate cover bolts and wedge that green wire in there, or (shameless but relevant plug) buy one of my
Ignition Keylock/Wiring Upgrade kits.
It takes the white magneto wire out of the equation, cleans up all wiring, and again, provided the button is good, gets rid of it's wire at the CDI (the black box your fat wire to your spark come from).