I could find a wiring diagram if you could post the model number under the seat. you will have a cutting blade disengaged switch, a brake switch, seat switch and drive neutral switch. When you are sitting on the seat with brake applied blades pto disengaged drive in neutral 12 volts positive travels through the switches and applies 12 volts to the small wire on solenoid which closes the large contacts inside the solenoid Applying 12 volts positive from the battery through the large wire on the solenoid to the starter. A good ground negative must be at the solenoid mounting bolts for the solenoid to complete the small wire circuit to energize the solenoid. Also check for good connections at the battery with no corrosion on the battery connectors.