Hi,
I found how to test the switch; have it plugged into the harness and with a voltmeter check the large wires to the chassis or battery minus terminal. One will be the power coming in, with the switch on one will be the power going to out. When the switch is moved to the start position there will be power to the starter solenoid. I did replace it and that still did not fix the problem. I ended up smacking the starter solenoid with a hammer and it started right up. It looks like I need a new one.