Hello,
I am repairing my son's 1999 XJ8 for my grandson to drive. The car had many problems but I wanted to relate this one to the group as I have never seen a thread on this issue.
There were no lights in the interior except for the instrument cluster and the radio. All the lights for the buttons and the lighted J shifter did not work. These would be the bulbs for the window switches, the radio buttons, the climate control buttons etc. I searched that circuitry on figure 10.2 of the 1999 schematics and also traced the power back to the LH heel box 5A fuse #3, (Fig 1.2). That fuse was blown and it promptly blew the replacement. I disconnected things the were fed from the dimmer control module at FC23-7 and FC 23-8 and replaced the fuse each time as I disconnected something. I started by disconnecting the 8-way connector CA224 that is located in the LH heel box and is fed from FC23-7. (It's a green plastic thing) which did not clear the problem. I then continued with the items from FC23-8. It turned out the circuit board under the J-Shifter was the culprit. I replaced that board and the fuse did not blow again and the lights that were not burned out came on! I also soldered in new bulbs in the J-shifter board and these now illuminate as well as most all the various bulbs shown on Fig 10.2. Finally I replaced the other blown bulbs so all the button lights are illuminated as when new.
I'll send another post with the replacement bulbs I use after this one.
Best, Dave