Eternal Coolant Temperature Sensor Question

All,

I have looked at many threads trying to find a consistent answer, but cannot. I am trying to find where and which "sensor" is the correct one for the water temp gauge on my '82 Mondial 8. Please note that my engine has been revamped to EFI and modern ECU so all sensors are different. However, I want the "water temp gauge" to work.

1. Terminology: there are sensors which I believe have a single wire (the other side is to ground via contact with the motor block) and there are switches which usually have two pins/wires (i.e., when they get hot they make contact, or not). Correct?

2. My Mondial 8 had a "thing" near waterpump housing -- I am using that threaded hole for a modern coolant temperature sensor for the ECU.

3. My Mondial 8 has a "thing" on the motor block in the valley (very hard to reach) and it has two wires -- the original is still there, thus a switch I presume. I am not using.

4. Coolant overflow reservoir has two "things" there that I am not using. It also has a "float" for coolant level sensing which I am using.

5. The radiator fan thermoswitch is a different thing that is being used, BTW.

I consulted AWItalian and they advertise Ferrari part 100453 and 104628 as the water temperature sensor/switch, each has only 1 pin. Not sure why two part numbers. I have them in hand (new).

** Since I cannot figure out what is correct, my thought was to "add a bung" to the aluminum coolant piping for either 100453 or 104628, run the wire to the gauge (I know which that is) and then also run a ground wire from the bung to ground. **

Help? Thoughts?