Chevrolet Repair: 99 Chev Suburban time delay interior lighting, light timer, timer module

Question
'99 Chev Suburban. When the exterior doors are opened, the interior lights come on. They should go off after a delay. Recently the delay has been getting longer and longer until now they stay on all the time; unless I use the dome override switch to keep them off all the time.
  Any ideas? It's my wife's auto and is annoying her and therefore me.

 Thanks for reply.

Answer
Ouch Bruno,
I understand that "therefore me" part.
I just don't have any experience with that light timer.
I bet it will require a timer module, but I would like you to ask someone with more experience than me on that.
Here is a link where you can find someone who will know.
http://www.chevytalk.org/
Go look around there.
If you sign up, and it is totally free, you can actually do searches, and ask questions. Great site.

Van