Do you mean the back seat light?
On my 1998 XLT the front seat, back seat and cargo area lights all turn on at the same time, like when the doors are opened.
My back seat light has a central lamp for general lighting as well as two lamps that can be turned on by backseat passengers via switches on the lamp. I have not had to change the lamps in mine, but I did open it up last year to clean the lense and reflectors when I was detailing the interior. I used a very thin pocket knife blade to pry the clear plastic lense off...but be careful and take your time as you want to avoid breaking the tabs that hold the lense in place.