In my bathroom, I currently have: one electrical outlet, one light fixture, and one fan. There are two switches at a 2-gang box (for the fan and the light). The fan is a simple fan without any other lights or speakers or anything.
I already set in the new light fixture and ran the wires through the attic. I am about to fish them down to the light switch box, planning to change it to a 3-gang and add a third switch.
But I found I don't quite understand the existing wiring. Specifically there is a red wire hooked to the fan's circuit in a way that is confusing to me. To accomplish my task, I was just going to wire a new switch to connect to the hot "line in" as well as the light, with the white return from the light going to the rest of the whites. But I wanted to make sure I understand the rest of the wiring.
Here's are diagrams: 1) what I observed in the box, and 2) what I infer is going on as well as my question regarding the wiring.