If engine cranks when the battery is connected to the small terminal on the solenoid, the solenoid itself, and the heavy wirng to the starter is obviously OK.
It sounds like you have a safety interlock problem - usually it's the brake switch, as it gets the most wear. The seat switch is not usually in the start circuit, it's connected to the ignition cut-off. The cutter deck switch is also a possibility.
phil_saunders@bigfoot.com
Phil Saunders
June 2008