cooling fan questions

[Meatman]

Sorry if this has been covered already but my Girly is loosing her cool.  Hot days in the summer time traffic is the only time she heats up and I mostly blame the cooling fan for the heat because the fan is not turning on.  I ran some tests on the wires, got the fan to run so the wires check out.  No busted fuses so there's no problem there.  I checked out the switch and it seems to be out of whack, so I ordered a new one. 
The question I have is, when we jump the wires from the switch to the fan circuit the temp gauge heats up, but the fan does not turn on in the run position.  As I let the gauge hit the hot point, I turn the ignition off and all of a sudden the fan turns on for a second then shuts off!  Anyone encounter this problem before?  I am sure when I get the new switch it should be back to normal, just curious if I'm missing something.
There are only 4 wires in the circuit, two from the fan to the fuse panel, then two out to the switch.  There is no radiator coolant temp gauge, only the switch in the thermistat.
Thanks!

[motoOzarks]

maybe thats because you're from Mars

[Bixxer Bob]

Shorting the coolant sensor to the fan (or anything else ) is of no use because there is no direct connection between the fan, the gauge or the sensor.  The ECU reads the sensor voltage and decides when to turn the fan on and what the gauge should read. 

Your decision to replace the sensor is good, but also check the contacts in the two big plugs on the ECU.   The ECU is known to corrode and throw up all sorts of issues.  If yours is in good condition, take the time while you're in there to duck tape all the holes in your undertray, including the ones under the ECU to help keep the water out.