Sorry I don't have pics, but it's on the roof, centered next to the windshield. Little black orb mounted in a factory plastic casing. 91 XJ, and the headliner has been removed prior to me getting it so if there was something on there that explained it, it's gone.

 

eh gonna need a pic to fully understand what your looking at

 

I know what it is and I've never seen one third time this year I've seen some ask its for remote entry

 

Yup, that's the receiver for the old infra-red remote keyless entry system. Very limited range, basically line of sight too. Better to replace those old (expensive, hard to find) remotes with a new RF (radio frequency) system with better range and much cheaper remotes. I used one of the Valiant basic keyless systems from JC Whitney for about $35 - $45. Splices into the wiring in the driver's door and box mounts on kick panel or under dash.