I don´t know if your XJ has AC or not, but on my wifes 87 (no AC) and at least one other I´ve seen. There is a cable mechanical actuator, to the defrost/foot warmer door (passenger side/under the dash). A push on type retainer, that pops off, the end of the cable just flops around, the default position (with the cable off) seems to be defrost. Also has a plug on top of the heater controls, under the radio. It looks like an electrical connector, but is actually like three vacume lines, that has come loose on occasion (can usually hear it hiss with the motor running). Had a cut line to the vacume resivoir, that seemed to mess with the heater controls also.
I´ve never had much trouble with the door panels, take my time and pry near the plastic clips with a large screw driver with feeling (don´t scratch the door). The arm rest needs to be rotated 90 degrees for removal on many models (which will drive you crazy if you don´t know). The door lock rods and inside handle rods, can be a pain, need a thin screwdriver and perhaps a pair of needle nose pliers, to unhook/hook the clips. There are some little retaining hooks, on the rear of the door/window toggle plugs, that sometimes fall off. There is a rubber spacer around the rods inside the door that can become twisted up and make the rods stick. The wind guard is easier to cut open at the door openings and duct tape closed, than to try and remove it around the edges. While your in there, smear as much of the window chain/cable as possible (there is a slot on the outside of the cable housing) with oil (motorcycle chain oil works well) or grease (hard to get to, but doable and necessary), Lubricate the window runners with a dry lubricant, teflon or graphit, grease the inside part of the door catches. Spray the inside part of the door lock mech with a light lubricant (WD-40)(grease gets thick in the cold and makes things worse). I can get a door panel off in about 5 minutes and on in maybe 8, done it a few (hundred) times.
Old XJ´s will keep you busy, I just unfroze and serviced the rear window wiper on mine, replaced the speakers and fixed a broken wire on a window motor.
The dome lights going dim, remind me of a problem I´ve seen before. Look under the drivers side carpet and inspect the wires that run there. I could be wrong, I´ve been working on XJ´s for years (like 15) sometimes things kinda get foggy. Frayed wires under the carpet, will eventually blow some fuses, pretty sure it was the dome light fuse. Could also be a bad ground, one is behind the drivers side kick panel (a pain to get off and on) another ground is the left side, under/bottom of the dash, near the courtesy light, tighten the screw and check for good contact. I´ve added a bunch of grounds over the years, most black wires are ground, splice in an extra wire and sheet metal screw to ground, solder works best to connect the wires.
