1Safety switch button not depressed
Be sure deck is disengaged all the way, parking brake is engaged and operator is sitting on the seat.
Battery is installed incorrectly
The battery must be installed with negative terminal attached to black ground wire. Negative is identified by "NEG" "N" or "-" The positive terminal "POS" "P" or "+" must be attached to the big red wire which goes to the solenoid. Charge battery fully before installing.
Battery is weak or dead
Check fluid level in battery. If fluid is low, fill to just below split rings with water. Charge battery fully.
Replace with an automotive type fuse. Check for loose connections in fuse box, bare wires, and pinched wires.
Loose engine ground wire
Engine should have a black ground wire running from engine to frame or mounting bolt.