I had a 95 E320 and thought the dash lights had failed but there was a control on the instrument panel, a rotary switch, if I recall, and it had been turned off. Up on the left somwhere. I now have a 2004 E320 and I wish I had the vintage car back. It had more power, better MPG and far better quality interior fittings. And that awesome smooth straight six.

Finding this "There's two knobs in the instrument cluster, just near the outside temperature gauge (if you have one).

The left one, its a rheostat which changes the resistance of the lights from low to max. Sometimes it doesn't make contact and all lights go off..."