This is the wiring diagram to my 12V refrigerator.
Terminals C and T on the refrigerator’s control box activate the compressor and fan when the thermostat closes the circuit. There are 5V of power coming from Terminal T.
You need to mount the temp sensor inside the refrigerator (near the door, in the upper area of the refrigerator). Drill a small hole in the side of the refrigerator box (make sure this is a clear path!) and route the temp sensor wire out the box and to the ITC 1000 sensor terminals. If necessary, you can extend the sensor wiring with standard small gauge wire (I’d recommend 16 awg, very common and large enough so as not to degrade the sensor reading).
Connect the refrigerator terminals C and T to the ITC cooling terminals (doesn’t matter which one). Again, use 16 awg wire or larger).
Obviously, you’ve got to provide power to the ITC (you should have the 12vdc version). I’d recommend powering the ITC from the same circuit as the refrigerator (ITC is on/off when the fridge is on/off). Note, the ITC diagram on the unit does not indicate which terminal is positive and which is negative (1 is pos, 2 is negative).
Now, you just need to program the ITC for the desired temperature. Manual is pretty clear about that part.
Hope this helps!