I had a loose connection on the switch so I fixed that and the fan still didn't come on until I tapped on the switch itself. What is it inside the switch that makes it work? Are there any moving parts that can get sticky?

 

I don't think there are moving parts. Are you refering to the connector on top of the thermostat housing? If so, I'm having the same problem, and I had to go buy a new connector from GM, it was $20. Probably a good investment, so you don't overheat your engine so you don't have to buy a new one.