mower engine ground wire to where?

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Just finished installing a new (used) mower engine. Cranking fine but no spark to the spark plug. Where does the ground wire out of the engine ground to? To the solenoid? There are the two hot wire posts on the solenoid (one in, one out), a smaller terminal labeled S where the start wire from the ignition switch goes and another small terminal labeled I. Does the ground go to this terminal. I have the ground from the ignition switch (labeled M) going directly to an engine bolt.



Thanks,