Engine doesn't turn off when switched to off

I have a Yard Machine by MTD that will not turn off when I remove the key. I tested the ground wire and the wire that goes to the ignition coil for continuity and they all pass. I have also checked that continuity exists when the key is turned to the off position between the ignition coil and the frame and engine block and there is.

It is my understanding when the ignition wire it grounded it prevents the spark from generating thus killing the engine but it does not seem to be the case with mine. I have taken another jumper wire and connected one end to the ignition coil and the other to ground on the lawnmower with no effect. When the lawn mower is in the run position continuity does not exist between the ignition coil and ground.

I have purchased a new ignition switch but that changed nothing.

Any ideas???

Thanks!

Engine doesn't turn off when switched to off