W123 Instrument Panel Lighting

I have a 1982 Mercedes 300D turbo and I can't seem to get the instrument panel lights to work.

All the idiot lights work, as do the turn signal indicators, but no lights illuminating the instrument panel, window switches or climate controls. I have replaced the rheostat, no change. I replaced the bulbs in the panel, no change. I removed the new rheostat and directly connected the two connector posts (pins) which are normally covered by the rheostat, no change. Does anyone have any suggestions for me? I need to get these lights working...It is really dark in there at night!