Operator Presence Relay.
Either a bad relay or poor connection to it from the seat switch.

With the key in the ON position-
Load/unload the seat. You "should" hear it click.

You can disconnect it to see if the engine will run, but you won't have PTO function.

There should be a GREEN wire going to it from the seat switch. Closing the seat switch provides 12V to the relay to "activate" it.

Here is a link that might be useful: Click here

This post was edited by bill_kapaun on Tue, Jan 27, 15 at 9:27

Look in the center of the seat switch plug. Is there a button in it ? It has to be completely depressed when plugged into seat switch. You can take a small screwdriver and tear it out if needed. This is a tamper switch to keep people from unplugging it.

See if governor is jambed or has come loose. Be forewarned,don't bend nor adjust unless you are absolutly certain you know what you're doing,governors are very touchy and easly mess up.

Mowerking- You should look at the schematic first.

It DOESN'T function the way you describe.
No shorting connecter involved.
This NO switch delivers 12V to the OPR to unground the kill wire AND complete the ground to the PTO.

It's a good thing to know, but as Bill said -doesn't apply here. Grey switches are normally closed and will many times have them. Green switches will not. Now, was the proper switch installed....

At least he has the old switch to put back in!

Probably a moot point since the OP hasn't had the courtesy to respond.