Pull the switch out and use a piece of wire to jumper the switch and see if it runs. If yes, it's the switch. Next I would suspect a bad connection. There should be a mini circuit somewhere connected directly to the battery and these can go bad, esp. if exposed to moisture. You *could* try using some long wire like say battery jumper cables or some #12 min. and connecting the battery directly to the motor wiring at the slide switch which would bypass connections between switch and battery. You could also use a voltmeter and see what happens to the voltage at the switch when you try and run the motor. Last would be to check the motor. If you were to take it out, I'd try jumpering 12 volts directly to it's terminals before you take it to a shop or get a new one.