Go to the Dometic website and download the User/Installation Manual for your reefer.
This is my NDR2610. The wiring is generally the same among the models. Near the back of the manual you will see a wiring diagram. The thermal cutoff device is wired into the 12 power source to the control board. Item "W". Basically what happens is when the flue gets too hot (such as when the refrigerant leaks out) the thermal cutoff disconnects the 12 volt power to the board. This cuts off both the gas and AC power to the electrical element.
