Ed brings up a good point. If the center console lights come on and brighten/dim with the dimmer, then your dimmer rheostat is obviously good. If not, dimmer could be bad or the center console lights may not be in place, as happened in my '89 wagon.
Probably you should pull the rheostat and check with an ohmmeter in the full bright position. If no continuity replace or, better yet, bypass the rheostat. Then if you still have no dash lights, pull the cluster and replace the bulbs. As herb mentions, they are pricey. I think I paid something like $12 apiece at Volvo for these.
If center console lights are out you'll have to remove the fasteners that hold it in place, pull it back and reinstall the bulbs if they're just out of place or replace them if they're burned.
All of this stuff is pretty easy. If you need further instructions, post back.
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'80 DL 2 door, '89 DL Wagon