>it was probably because something was fucked (maybe the switch, maybe the fan) and the old owners didn't feel like fixing it properly

That very well could have been the case - that old owner being my 80 year old dad. He may have attempted to disconnect the switch, not knowing how to do it properly when the fan went out. Pretty sure he didn't know it was a switch-loop either. He's a chief navy mechanic and is brilliant with automotive and almost anything mechanical, but, admittedly electric wasn't something he ever got to focus on. Which is part of the reason, I'm trying to learn a bit.

I'm in the U.S.

This is helpful though. I'm going to pick up a multimeter tomorrow to test. I had a voltage tester that only told me if there was any type of voltage.

There is. Switch loop seems to explain it! Also explains everything else to some degree. Like why that smart switch didn't work. Still working it out in my head though. Thanks for your help!

Alright. Makes sense.

Yes. It appears to be rubber. House was built around 1940. Parent's house.

I looked up cab tire but didn't find much. Is it dangerous? Probably not in the budget to rewire the house just yet, but would be good to know to line up priorities.

Whoa. Looking up switch-loop = mind blowing. Thanks for illuminating that for me. It's all starting to make more sense.

Got it. Makes sense. I'll also google switch-loop to further understand what's going on.

Would my original normal switch work?

If so, did it make any sense that the green ground wire was connected into the old switch... and the white wire connected as well, but the black wire coming down was disconnected?

Thanks for your help. So just to clarify... as is, the wire coming down will not work for the dewstop switch as I need another hot wire to connect to the red "fan" wire?

If it's incompatible, will that original switch work?

Well, I bought a new fan, a Nutone 696N, which has green, black, and white wires that I need to connect.

The original fan was connected to a wire that seemed to go down directly into the house above the bathroom wall. That was kind of confusing to me cause if it goes directly to that switch, it would have never worked... cause where would the power come from?? There's obviously some kind of junction box between the fan and switch, but will attempt to trace that wire to be certain what's the going on.

Seems a doable project according to many YouTube videos and articles.

I don't think it's extension cord wire. It's an old house so it's whatever what was coming down into the old switch. I assumed connecting the white to the white was neutral, but from your response, I guess not.

So, are you saying the wires coming down are incompatible with that switch, despite being black, green, and white?

Admittedly, though I'm an engineer and come from a mechanic family and work on cars, I know next to nothing about electric other than YouTube and a book i purchased, but planning on taking a community college course. And hiring an electrician if I can't figure this out myself.