Well the Jeep gods are doing their thing, sometimes good, but mostly poltergeists.
OK you found the "switch" and disconnected it. I'm thinking someone wired in a parallel switch to power the B.U. lamps to provide rear lighting, did this once to help see when launching / retrieving a boat.
Open either taillight and check the voltage on the bulb. (after recharging the battery) Then check the BU fuse for voltage, I think it is only hot with the ign on, anyone else have any ideas? Then start looking for add on stuff that you have no idea what it is for.
I no longer have any prints for your model year.
Hope this helps a bit