I think I figured out what it is:
From the documentation I received from Thor earlier, I got this electrical diagram:
It appears that "CC" is what I found. It is called a "mini-breaker" on the diagram, and it appears to be on the input to the converter.
That is all well and good, buy why they would put it in the lavatory is a mystery to me, unless of course it fits my theory about connecting an inverter.