If you are talking about underhood engine cooling fan, it use not thermo switch but thermo resister sensor, which located on the right side of engine, just behind the drive belt (if you will see from front of vehicle it will be left side). It’s for 5,7 HEMI engine. But if I remember correct, if you unplug the sensor, fan will start immediately. Also wires from the sensor connected to ECM, not the fan directly, so don’t try check it with 12v.