In response to Facebook post (below), Jorge wrote...
A general outline:
I expect the heat temp sensor is two wire. Typically, the circuit layout is like this starting from power to ground:
Regulated power source > Current limiting resistor > Signal tap (the tap for the PCM logic to read the resulting voltage) > Thermistor (two wire) > Ground.
In this configuration, as the thermistor goes lower in resistance the voltage at the TAP goes down. As the thermistor gets higher in resistance the voltage at the TAP goes up.
Keep in mind that this example, although typical, might not represent the circuit you are working on. Therefore, it is always best to refer to the wiring diagram for the vehicle in question.
Next. The test tool is simply a potentiometer. Two of the wires go to either ends of the resistor. The other wire goes to the wiper. Use your Ohm meter to locate one wire on an end and the wiper wire.
As the dial is moved, the resistance will change. Check the dial to see if it is close to the Ohm meter reading. Does the Ohm meter reading go up when the dial is moved to a larger number? If instead the Ohm meter reading goes down move the meter lead to the other end wire.
Perhaps the next step is to check the specs for the specific circuit under test - min and max resistances. Use your Ohm meter to get an idea of where your dial is and what it takes to dial through the desired range.
Next, while still connected to your Ohm meter, set your start range/position. Check the dial and see of it is close to matching the Ohm meter reading.
Replace the thermistor with the potentiometer and connect to the same wires the Ohm meter was connected to. Start circuit. Move pot. Monitor with scantool.