The temperature sensor is the copper tube descending from the cold well above. The copper tube leads down to the thermostat. In front of the thermostat is the power switch.
To remove the thermostat from the power circuit, we disconnect it's top connection (wire 4, label not shown) and disconnect wire 2 from the power switch.
Wire 4 is moved to the power switch terminal that wire 2 previously occupied. Wire 2 is kept out of the way by looping it back to the thermostat's top terminal.
New control components are installed on the middle shelf.
The control computer is back left (blue). Power entry and switching happens on the rail of components at bottom right, including safety features like a circuit breaker. All of these components will be miniaturized as development continues.