I hope this is simple. I want to add a GFCI receptacle on the wall of my bathroom behind a medicine cabinet. The closest electrical is a switch for my bathroom fan. Even though we have just one switch, it seems it was wired for separate control, because we have 12/3 wire coming into the switch box. Neutral is capped and red/black are attached to the switch.
Can I tap into this for the GFCI receptacle? I had trouble finding a matching diagram even though I know this is a common configuration (12/2 into fan then 12/3 to switch). How does the circuit work right now before I make changes? I will likely retrofit the bath fan soon and would like to have separate control.