Yes indeed, those potentiometers give trouble sometimes. I really don't understand how they can possibly burn out since the dash lights are so dim you could probably measure the current in microAmps.
Since the max setting isn't bright enough anyway, I just solder a jumper across the two copper strips on the back of the potentiometer, to give it a solidly reliable max bright.
If any of the other instrument panel lights besides the instrument cluster illumination itself are working, then the pot is making contact, in which case, yes it probably needs illumination bulbs in the top of the instrument cluster.
BTW, you don't need hooks to remove the 123 instrument cluster, simply remove the three trim pieces from the bottom of the dash, behind which are three phillips screws, remove them and the two phillips headed plastic retainers at the bottom of the lower panel cover and lower the cover, don't remove it, it's a hassle to put back in place. With the cover lowered reach behind the instrument cluster and simply push it toward the steering wheel. Occasionally it will try to hang on the plastic that surrounds it.
Once you have pushed the cluster forward far enough, you probably want to take it the rest of the way out and do the instrument bulbs or potentiometer work on the workbench. To get it completely out, disconnect the master electrical connector to the left of the speedometer, then using a 13MM open end as back up and a 10MM open end on the oil pressure line remove it, then remove the thumbscrew for the speedometer cable. There will be three more wires at the lower right of the cluster, pay close attention where they go, then remove them. The instrument cluster is now free.