Comgrats on 300D!! Re. no instrument lights, had same prob. with my 81 300D purchased about 2 months ago. From my 15-year experience with 80 240D, however, I remembered that the dimmer may be turned down. Dimmer is left one of the two small, identical knobs protruding from bottom of instrument cluster; larger, black, key-looking knob farther down and to the left is the manual idle speed adjuster. In the dark with the car lights "ON", turn the small dimmer knob back and forth slowly and see if you get instrument lights. 'Did this on mine and suddenly had instrument lights, though still somewhat dim for my liking. Pushing the same knob resets the trip meter (lower part of odometer). Small knob to the right is for setting clock.
BTW, my 81 300D does have the idle speed adjuster just like the 240D. Good luck!!
91 350 SDL. 81 300D