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xkcd #2848: Breaker box
(imgs.xkcd.com)
Alt text:
Any electrician will warn you to first locate and flip the house's CAUSALITY circuit breaker before touching the CIRCUIT BREAKERS one.
I'm betting your house used to have a 2nd bath or was going to get one but was abandoned. The fan was likely the bathroom 2 or possibly a range hood.
All brown wires is definitely what's incorrect. Hot, neutral and ground should be easily identified at a glance (black or red for hot, white for neutral, green or bare copper for ground where I am). I've only ever seen brown sheathing on older fabric or paper insulated wiring.
I am not an electrician and this isn't advice.
Where I am brown is live. So they're all live wires apparently.
The house was built in the early 1920s so I'm not surprised that it's weird. It was built before homes really had electricity or indoor plumbing so the wiring and bathroom were added after the fact. Combined with the fact that the previous owner did a lot of DIY and weren't very good at it.