Were not grounding anything here. The way the electricals are set up,pushing the kill button grounds out the white wire. Grounding the white wire is essentially shorting out the magneto!
What were doing is having the wires just as they are. Connect coil to magneto Blue to Blue,Black to Black,white to accesories like lights or cap it off.
Now on the blue wire,simply attach a toggle switch. No grounding. Wire to wire.
When your running your bike just like in your car,the switch is ON. When you want to kill your engine,turn your switch OFF.
The way happy time has it is all backwards. Push the button ON to short out the white wire.
....I dunno. Maybe it's a China thing.
This is even the way motorcycles do it.