This goes beyond the mystery switch on top of the steering wheel pod.
You have to have the key in the ON position to work the power windows, but the heated seats work in the ACC position.
I spent the last week doing contractor watch, mostly sitting in my '00 OBW and watching other people work. (personally it's more work than doing something).
I'll admit to listening to the radio.....
I caught the almost dead battery syndrome three times, by turning the key ON to roll the window down and forgetting it (which brings the damned Daytime Running Lamps on).
My aftermarket stereo would drop out, then the car would barely crank if at all. Thank Ghu that a 2-5 minute "sit" would get enough crank power to start it again.
After tattooing "Shut The F***ing Key OFF" on the back of my hand ;} I proceeded to check other draws and conditions. Sure enough, the heated seats are live in the ACC position.