[Brittany Dogs]

To me, this does not look like a factory installed switch. Wild guess - it is a master switch to cut power to the furnace. The thermostat has an on-off switch in it by pushing the temperature lever all the way to the left past a detent.

But if the previous user would forget to push this lever on the thermostat each time they closed up the unit, the furnace might have been able to cycle on. So my guess is, the previous owner wanted a larger switch that was obvious as to what position it was in (off) when they closed up the unit.

My TrailManor unit will cycle the furnace even with the bathroom wall stowed away (releases the master kill switch) and I had the above concern about the furnace.

So take a look behind the panel and see (or feel) if a wire or two goes from the ivory household switch and goes to the thermostat.