The red lit switch is something that was added to the boat by a previous owner. Not standard equipment. So only a guess. Maybe a light switch for the a light in the vicinity? But it could be for a hundred different things. If it is a light fixture and the bulb is burned out, it'll take a while for you to look around and maybe find it.
Hint for new members: your personal profile should have as much info as possible as the make, model, year, size all can help us answer your questions. A photo of the boat is a nice touch as well.