[76Red18]

i would say the switch is for a macerator pump which grinds the leftover ice, guts, scales and then pumps the "sludge" to an above the water line through hull fitting, probably the one closest to the box. The pump should very close, if not attached to the drain. They burn out easily, so the previous owner might have removed it and just drained it to the bilge. I'd get a new pump if that's the case.