Am I to understand you fitted a radio transmitter style keyless entry from say a '97+ into your '92, replacing the IR system?
Not exactly - everything I found online indicated that the 97+ XJ keyless system was dependent on the BCM (body control module) and if you didn't have at least one remote already programmed to it, a dealer scan tool to program remotes.
What I actually did was swap in the keyless entry module from a 95 Chrysler Concorde, which is RF-based, but self-contained (supply +12V to one line and pull another to ground, and it goes into "learning mode" all by itself). I based my work on this link I found:
http://www.jeepforum.com/forum/f13/ir-rf-keyless-entry-conversion-676076/
Where a fellow did the same change to his ZJ. Seems 93-97 LH sedans (and, supposedly, some RAM pickups in that general period)all used this particular self-contained module.
All I had to do was pore through the wiring schematics in my FSM to figure out which lines to splice to B+, Ground, Unlock Relay, and Lock Relay on the harness in my XJ. Turned out to be really easy - the module slips between the roof and headliner nicely without rattling around, and with fresh batteries in the remote (found a RKE module and fob as a matched set from the same vehicle for about $30 on eBay) I can now lock/unlock my Jeep from as much as 30 feet away. For the moment I have to hit the unlock button twice, but the RKE module has a separate line for just the LF door as well - I'm thinking of either tying that into the unlock relay line too with a diode, or trying to run a wire down into the LF door and create a LF-only unlock function (will require some sort of diode since it looks like it's a single supply voltage fanned out from the relay to all four doors), but I'll worry about deciding that after NACFest - the original XJ functionality has been replicated, and that's good enough for now. I also need to set up the two SPST switches I bought to make entering learning mode easier (right now I did it with crimp-on QD connectors, but that's only temporary).
Looking back, I'm not sure how I'd have gotten the module tucked up into the headliner had I stayed with my original piece, though - the dome light hole might have been too small. Fortunately, my original liner was shot and I had the 97+ one ready to go in, so now I just have to drop the front domelight (which is bigger on later models) to open my "service port".
Since I saw over in the other forum you're coming to NACFest, you're welcome to track me down and have a look.