FYI.
Just ran into issue with M73 and 336R100 Thermal Sensor with Mx-O-M7SA-8D100.
IMG Sensor connected to Cable 1
Thermal Module connected to Cable 3
The thermal module was not detected.
We found that disconnecting the IMG Sensor and leaving Thermal connected to Cable 3, booting camera and once the Thermal module is detected. Power camera down connect image sensor
Boot camera and go to SETUP → General Image Settings → Camera Selection will be visible and you can choose BOTH, Overlay or whatever your task requires.
Keep on truckin’