I have a 2002 Grand Cherokee Jeep and the issue is that the radio/clock display is blank 99% of the time even though everything else on the stereo works fine (radio, cassette deck, 10 CD changer etc)

check fuses and connections

check fuses to radio.
check connector at radio.
if all that is good, radio is bad.

all you can do with magic is. (no books)
1: check fuses.
2: check connection.s

sounds like there is a loose connection to the radio that powers the display.you don`t say if you get sound from the radio.it could be an internal connection problem,like a bad solder joint.you should be able to have the radio repaired or you could have it replaced

If you want to solve your problem, click on the link I attach
https://www.reliable-store.com/products/jeep-grand-cherokee-wj-wg-99-04-workshop-repair-manual-download

You co0uld change the module but I don't know the exact location of yours (under the dash) If I was working on it and couldn't get a location, Id take a look at one from a parts house so I had an idea what I was looking for, then start looking. They aren't cheap though so sometimes it's best to have a good shop look it over just to make sure it will fix the problem.
When working, I test everything either with meters, scanners etc or use known good units to check problems. Here, I can only make educated guesses. Electrical parts are generally non-returnable so mistakes can be costly.
Good luck though.

Jeep radios are notorious for having display and channel issues. If your display is not operative, then your radio internally damaged and is not worth repairing. It is better to replace it at this point.

the problem is you dont have the battery wire on the radio hooked up to a 12v constant. it sounds like you have to take the battery wire of the radio and hook it up to a wire that stays 12v all the time even when the car is off.

Hello
Welcome to FY
This will require removal of the radio and taken to a repair shop to replace the display,
Here is a link for repair.
http://www.carradiorepairs.com/?gclid=CJuI1eDXiZgCFRKLDQodkTwFDQ
RD

I found a solution that sounds reasonable at another site: http://www.automotivehelper.com/topic177704.htm