If you short that black wire with the green arrow going to it, to ground- a piece of non painted metal on the bike- the engine should stop.
If it does not stop, your wire is not connected to your magneto.
If the engine does stop, your switch is either not making contact between it's own contacts, (bad switch) or not routing the power to ground- (insufficient ground coming from your switch to whatever the it's grounded to. If your switch is a one-wire switch, it should be grounding through the switch.