X2 on going only for the Factory Service Manual from Mopar, Chilton's and Haynes are both nearly worthless beyond changing spark plugs or the brakes.
Odds are your instrument cluster only has a flakey connector behind it. It has two large multipin connectors that especially on earlier TJs, are well known for knocking out the instrument cluster.
Here's a link for how to make sure the connectors are making good solid electrical contact. Basically, it only involves removing the cluster (easy!) and tweaking the male connector pins slightly to help them make a better contact with their female connectors.
TJ Jeep Problem with Instrument Guages.
My only suggestion is that instead of "twisting" the connector pins in the writeup, I would just give each one a gentle (!) squeeze to make them just a tad/tiny bit flatter which will help them make better contact. I did this to my '97 TJ 12-13 years ago and it permantently fixed its instrument cluster that would intermittently go dead.