no spark on riding mower?

I have a yardman riding mower. I have replaced the ignition coil many times (8) and I still get no spark. The engine spins over so doesn't that mean all of my saftey swithces are in working order? I have even disconnected the black ground wire to confirm that it's not shorting out anywhere. The magnet on the flywheel seems to have good magnetic pull. I have set the air gap at the recommended specs and got the correct gap at the spark plugs. I have even put a ground cable from the cylinder head back to the negative side of the battery to make sure I had good ground. What else can I do? Can the problem be in the key switch? I thought that if the fly wheel spins the magnet passsing the magneto it should create park and I have none.