Wow I'm surprised no one is flaming you over this post! Gotta love JeepForum.com, everyone here is really nice with us inexperienced people. Ok so this is a very common problem. You basically got 2 elements working, the gauge and the fuel sending unit. First, I would try to remove your instrument cluster and sand the terminals, this is the easiest fix. Here is the link for that w/ pics... http://www.jeepforum.com/forum/f12/r...er-how-991307/
. That worked for all my other gauges, not my fuel gauge, which I'm still struggling with. Here is a link to a 93' YJ manual that has all the diagnostic info you would probably need. http://www.scribd.com/doc/13985775/M...cina-YjXj-1993
. Page 22 is where you will find the gauge diagnostic information. Now the manual is for a 93, I have a 90 YJ so some of the specifications were different for me. On my 90 here is a resource which tells you how to diagnose the gauge as well as wiring schematics etc... http://home.sprynet.com/~dale02/misc.htm
. From what I understand, if the needle goes all the way to full this is almost always a ground issue, and mine does that intermittently but normally my problem is that it wont drop under 1/4 tank.
Good luck and I hope this helps!