Green lamp in place. Note it is connected to the output of the Thermostat,
 [Under the white insulated cover] which will indicate each time the thermostat turns on the fridge.

The orange covered wire is connected to the 12volt switch to the left of the photo tapping off 12 Volts for the lamp located to the right of the fridge, out of the photo view. The blue negative wire is connected to the negative terminal from the battery input connector, which can be seen at the top of the photo.  This voltage is turned on every time the engine is running and at no other time. As this is not connected to a thermostat, by default of the manufacturer,  the fridge is at maximum     * all the time the engine is running, so the indicator lamp is illuminated as long as this switch is on.

   *Actually the 12 Volt supply will never give enough for freezing and should be considered a cold box while travelling.