Tachometer issue

The YJ uses T5 and T10 dash and indicator lights. Amazon has LED versions cheap in multi-packs. They work great. Here's the ones I got, but they make colored versions as well.
T5 Bulbs
T10 Bulbs

Not sure where the early YJs got their tach signal (negative side of the coil or an ECM), but the tach's power is a completely different circuit from the dash lights, so if neither are working you either have two different issues, or the problem is something they have in common: The connector at the back of the instrument cluster.

I've got a newer rig, and had to go look at how the 89 did things. It's a pretty simple circuit, and the White/Black wire that powers the tach also powers a bunch of other things including all the other gauges, so if they're working that's probably not the problem. The Orange/Black wire powers the dash lights, and it all grounds through the black wire. Assuming the two power wires are energized when they're supposed to be, I'd try a jumper to ground first on the case of the tach and then tapping the black wire at the connector. That's about all that could be wrong with the dash lights. The green wire supplies the tach signal from the ignition module... not sure where that is on your rig.