XJ's up to a certain year have the wiring for the clocks... Althought they are different. Up to I think 91 or so has it. Jeep stopped making the clock cause they're on the new radios... I got a wiring diagram for a 90 and theres 2 different model clocks that they used for the 90's. It depends on the radio. The connector is made to accept both models. My base XJ didn't have a clock from the factory and I added it. I got one out of a 88 and the wiring was different. I have to open the connector up and move a wire so it would dim when I put the head lights on.
If you got a newer XJ that doesn't have the wiring. Like I said 91+, the wiring isn't there. The easiest why to tell is if you had a factory radio did it have a clock. If the clock was there then you don't have the connector. All the clock really needs is 3 wires. Power, memory and a ground. The ground is easy. Power, use the wire that goes to the lighter, it only works on when the key is on. And a constant hot for the memory use the hot that goes to the radio. Its easy to pull the wire over. The 4th isn't needed but if you want it to dim when the headlights go on use the orange and black wire for the light for the lighter. Its a orange and black in the 90's. I believe all the AMC Jeeps use orange witha black tracer for the interior lights.
If you have any electrical questions as far as accessories go let me know. I have a base 90XJ that I've added alot of features to by raping stuff out of junkyards. Power windows, power locks, overhead console, the full Jensen audio system, High Line gauges, fog lights, even the light for the lighter... I also have a Mitchell book with wiring diagrams for most years.