1. Instrument cluster bulbs burnt out, or failed dimmer rheostat. rotate the knob back and forth 20 times, sometimes fixes it.
Do the other cabin lights work? dome, console & shift lights? if not, check fuse box under hood. Headlights on different circuit.

2. Its your problem now. take off panel to inspect next time you are bored.

3. My sedan is same way. I put a dog blanket on my legs for long trips. Would love to have an answer as well.

4. there an empty spot near the pump? maybe some fastener holes on fender? will check car in AM if no one chimes in.

5. nubbin controls passenger mirror. switch could just be crapped up.
I have to pull the panel & clean out window switches etc every couple months. I blame the dogs. Panel not difficult to remove, but there is a trick to it.

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1991 300D