'90 radio display dead

OEM am/fm cassette. No display. Radio works fine. Is there a lightbulb someplace, or is it dead? Not even a faint image.

There is a relay behind the driver side kick panel that controls the on/off of illumination of the clock and radio display. The dimmer is controlled by turning the headlight switch. Clean the contacts of the relay. If that doesn't work replace the relay. The next step, if the preceding doesn't solve the problem, is to trace the blue and orange/white wires (connecting to the back of the radio) for open circuits. If it is mechanically tuned (not electronically tuned) then only the orange/white need be traced. My experience is with an 88 Comanche and an 89 Wagoneer. When I dismantled my 85 Cherokee I found that the reason the light hadn't worked was an open wire but I do not recall its color.

If it's the radio that is bad, let me know. I just replaced mine (I think the OEM one works) I could send it to you for cost of shipping. If you need it I'll make sure it works before I send it to you. I have a 90 XJ Pioneer.

I just fixed my 88 MJ......maybe yours is the same....take out the radio, remove the top and bottome covers (I'm not sure which one is the correct one). Look right at the top edge of the display that is exposed by the cover removal. On mine, there was a tiny elongated bulb. You can see where the two end contacts for the bulb are soldered. Check across the two bulb leads for power, if you have power, but no light, the bulb is blown....
Go to radio shack and ask them for their smallest 12V lamp..they are about the size of a large grain of rice and cost .89 for two in a pack.
I twisted the leads of both of these bulbs together to put them in parallel, and soldered them in....worked like a champ.

Thanks, all. It's always "fun" trying to track these things down. If I read my FSM correctly (and that's a big "if"), the relay feeds both the radio display and the clock, since they both have the dimming feature. My clock displays and dims, so I think it's the radio. I'll yank it and take a look. I had one apart awhile ago looking for a bulb, but didn't really know where to look. I have had 4 or 5 of these, so I get confused sometimes as to what I saw and what was really there.