Check the voltage at the smaller wire that goes to the starter solenoid. Should be more than 11v, with the key turned to start, operator in the seat, both control levers out, pto off, and brake on (and all those switches working properly)-- and the wire still connected to the starter. Low voltage, there are a couple ways to fix...check your connections first off (the big white connector under the seat has been an issue more than once). If all connections are ok, you can install a John Deere starter relay kit which solves the low voltage issue. Part number on the kit is AM107421. NO voltage, check the switches. If switches are ok, check your starter relay which is under the seat, and check it's wiring for corrosion.