Where is the Engine Temperature Sensor located?

First of all, this is a custom built restomod of a 1938 Cadillac. It has a all new custom frame, suspension, rearend, etc. And it has the engine from a 2011 CTSV. I have a stand alone wiring harness made for this engine from PSI. When I start the engine, it is difficult to start and the engine runs rough and smokes. When I put a scanner on it, no codes are thrown, however, the Engine Coolant Temp shows -40. From what I understand, that could be causing my issues. However, I'm not sure which sensor is the engine coolant sensor. Based on the harness, what I thought was the ECT sensor has three wires and three pins. So, I don't think that is correct. There's another two pin sensor that I thought might be the ECT sensor, but when I bought a new sensor, although it kind of fits, it doesn't snap on to the harness. So, I don't think that's correct either. My question is, where is the temperature sensor on my 2011 Cadillac CTSV engine?