Sang's Sc kit uses a switch to activate the magnetic clutch. U can also opt to use an rsm/shift light to trigger it via rpm control. So, u'll have a something like a vtec. Hehe....
imagine doing that on a twin-charged car.
low rpm = supercharger on.
hi-rpm = supercharger off, turbocharger on
hehe

anyhow, i wouldn't use a manual switch.
shift light wud be my preference there. when the shift light is ON, you know the s/c is ON.
