Ok- - - - -some later model vehicles have a "self test" mode on the warning lights, but I'm not sure one of that vintage would have included that feature. Here's the problem with testing the "hot" section of the sensor- - - - -even boiling water will not get it hot enough to trigger the "hot" warning light. That's because "normal" coolant temps can get into the 250-degree range before the coolant starts to boil. That's because a pressure cap raises the boiling point 3 degrees for every pound of pressure and a 14 lb. cap is correct for your truck. That puts the "coolant boil" temp at 257 degrees. You'll need to use a heat gun or some other type of heat source and get the sensor up into the 250-degree range or so to see if the hot lead gets a ground. That will need to be done with the sensor removed from the engine so the sensor can be heated and the circuit checked with a powered test light or an ohm meter.

Edit: Sometimes the "hot" light self-tests while the ignition switch is in the "start" position. Check that out before swapping switches. I'm not really sure if any kind of dash light self test was used, however.
Jerry


"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
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