This is how the monitor panel in my '04 read the tanks in winter mode:
NOTE: When the water system is operating in the winter mode, only the interior fresh water tank is to be used.
Therefore you must be aware that the interior tanks fluid level is actually empty when the 1/3 L.E.D. light is displayed on the monitor panel.
The monitor panel will indicate that you have full tanks when you have an empty
exterior tank & a full interior tank.
Your monitor panel could be different than mine was.
I suggest testing it manually (ignore the panel). Switch the tank selector to the interior tank, close the interconnect, open the exterior drain. Once the exterior drain stops running add water to the interior tank and see if any water exits the exterior drain.