It is not clear from your post whether you are getting a spark at the plug or not. If you haven't checked please do so.

Likely the seat switch is bad/misadjusted or possibly disconnected.

It's hard to read the schematic for your mower but-
Sometimes disconnecting the seat switch will insure a no spark condition. Other times not. You might try disconnecting it to see if it makes a difference.

Well, I found it. I disconnected the seat switch but I still had a constant ground on the seat kill switch line. I traced the ground to the connector plug for the seat switch. There is a spring keeper in the plug that was contacting both sides of the plug. I removed the spring, reconnected the wires and battery and it fired right up. It was driving me nuts that I couldn't get a spark at all. Forums are great. Even if you don't get the answer you are looking for, you get to vent!
Thanks

The plug has what they call a "shorting connector". It was designed to defeat the users that were disconnecting the seat switch.
I haven't heard of problems with the plug being bad, just not seated fully.