This is a very old house. I wanted to add a light/fan to this bathroom while the ceiling was down for repair. When I opened the switch box this is what I found (second picture). A GFI wired correctly, with the switch for the existing vanity light coming off the GFI load side, however I’m not sure what the red wire is for. Since I need to keep the vanity lights and add the switch for the light/fan, I bought this Legrand Combination switch (last 3 pics) hoping to be able to use it to accomplish the switching without having to start cutting into plaster to install a 3 gang box.
Can anyone draw out or explain well how I can wire this up with what I have to work with, or suggest a better combination switch and how to wire it all up?