On cars with the Cool Harness mod, you can not test the default system for fan because the parallel resistor of the mod is still in the circuit [ bridging the sensor connector wires/circuit with a larger R value than the computer uses for trip]
Remove the mod , then unplug the connector from the ETC sensor , and see if fan then comes on.
If it does , you have a bad mod resistor/and/or connection...
When you short out the sensor , you are simply putting zero resistance in parallel with the mod resistor and in a parallel R circuit, the RT value is always less than the smallest resistor..
so this shorting will bring on fan as the circuit has now gone from high R to low[actually none] . This triggers the fan..
Do a resistance/continuity test on the mod Resistor...