Can you tell if it was "factory" installed or "user" installed? Usually, if you look closely at the cutout and/or the spacing (is it centered with the other switches, is it closer to an edge than the switch on the other end, ect.) you can tell. If it is factory installed, then you most likely can find a corresponding fuse in the fuse panel to whatever the switch controls by process of elimination. Most always, factory installed controller switches will have a fuse (12v) in the fuse box that mates with whatever line or device that switch controls. Try pairing the the labeled fuses with the switches that are known and whatever is left may be controlled by that "mystery" switch.
If the switch was installed by a previous owner, it could be almost anything, but, if I were to give a WAG on the probable function, it would be that it controls either add-on lighting (maybe a step light behind the stairs?) or possibly add-on tank or water line heaters... but, in reality, it could be almost anything, and if added by a previous owner, wouldn't necessarily be routed through the fuse panel. Most likely 12v though, if it looks like your other 12v switches...there are switches that resemble the panel switches used for 12v that will handle 120v, but, to my knowledge, none of the trailer makers use them for durability and safety reasons; a 12v looks like a 12v switch and a 120v switch looks like a 120v switch.
To be honest, I've never even been inside a 160, so I can't even give a real good guess and being an '06, no telling what "options" CruiserRV was installing at that time as they were still a relatively "young" company and there was probably a fair amount of ad-libbing going on with the assembly process. It is entirely possible that they were, at that time, using a panel that went to another trailer model, say a 210, and on the 210 it is functional (outdoor light) that doesn't even exist on the 160, so it doesn't go to anything. You could even pull the panel and see if it a) has wires attached and b) are the wires "hot"...that would at least tell you if it is supposed to control something or it is a "dummy" switch and doesn't do anything at all...
Sorry, great lot of help am I !!!