McCullogh timberbear ignition problem/question?

I recently installed a new 605 shortblock in a Mac Timberbear.
I tested the spark before completing the assemble and found none. The kill switch is connected to the coil tab and grounds the assembly to the motor,thus stopping the saw. But this doesnt make sense, since the ignition assembly is bolted to the oil tank that is directly bolted to the motor and seems constantly grounded. I have a brand new ignition assembly (thinking my origional was bad) with the kill switch connector tab grounded to the ignition assembly.
Question: how is the ignition assembly isolated from the motor and therefore allow the kill switch to ground the ignition assembly?
Thank you,Bill