`96 Cherokee -- what's this thing?
 

Bought a `96 Cherokee last friday, pretty happy with it so far (ti doesn't
even have the standard 4.0 oil leak) . But I'm wondering what this is:
Screwed to the headliner between the front visors is a 3" x 7" gray
plastic piece with a 1" diameter black plastic dome hanging down from the
middle. It doesn't light up, it doesn't turn, it doesn't do anything that
I can see. Whatizzit? Could it be part of a now-defunct alarm system
(siren and LED are in place, but I've no way to arm or disarm the thing)?

And: This Cherokee came in the Sport trim package, I'l like to have the
lensed overhead map lights like in my `89 Cherokee Pioneer. Can I just
pull a map light fixture in the local bone yard and plunk it in?