set park brake, turn key on put transmission in neutral a,d try to start it. If still the same thing then put it back into park and grab your test light and get under neath and have some one turn the key to crank and test for power on the small wire on the solenoid, if you have power there when the key is turned to crank and it goes away when the key is released then the starter is defective, if no light then it could be the park switch, ignition switch or a wiring problem, you will need to test each separately.
Or if you could just whack the starter with a small hammer while someone is holding it on crank and see if it starts the engine, if it spins then you know it is just the starter.
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