Dash cluster lights are out but the gages still work.
I don't think there is a separate fuse for the lighting in the cluster, so you may have an electrical issue in the cluster itself or the dash lighting dimmer. Usually there is one fuse that feeds the whole gauge cluster.
Have you tried the dimmer switch to make sure the lights where not turned down?
Sounds like the bulbs are burnt out. try slapping the dash fairly hard right above the cluster while the van is running with the lights on(easier to see it at night). If any of them come on(which does happen) then it's bad bulbs. The good news is I do believe they are replaceable. You have to take the cluster out and take it apart a little ways. Not very hard to do.
Looking for a Used Silhouette in your area?
CarGurus has 142 nationwide Silhouette listings and the tools to find you a great deal.
Search Oldsmobile Silhouette Questions
Oldsmobile Silhouette Experts