I am providing the starting circuit wiring diagram showing you there are 4 safety switches in the circuit from the key switch to the starter.
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The first place to check would be the seat which has two switches.
To prove the starter itself is OK you could "jump it." This has a serious risk as you are bypassing all safety features. My suggestion is to have someone in the seat with a foot on the brake.
Use a piece of wire or even an old screw driver to bridge the small terminal to the terminal with the battery cable. Expect a few sparks. The engine should crank instantly if the starter is OK.
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Dave