Temp sensor

[terbear]

I was cruising around town on Sunday, lots of stop and go traffic. All of a sudden my temp warning light comes on, yet the fan was not running. Once I got some air thru the radiator again, it went out.
When I got home, I let it idle in the driveway, and sure enough the light came on again with out the fan starting.
Later I shorted the temp switch that runs the fan at the bottom of the radiator, and the fan began to spin.

Question is: How does on know if the fan is staring to late, or if the temp warning light is coming on prematurely???

I know I should take it to the dealer, but I would have to put my original pipes back on, and, they would probably have to order a part, and leave it there for a few days, I live 90 miles from there.

Any sugestions?? Thanks Terbear

Is there an automotive replacement switch for the fan switch, I would rather spend 20 bucks on my own than bring it to the dealer.