86 Mercedes Benz 300 E problem?

Dash: first check that the potentiometer/dimmer switch is not turned all the way down. Assuming it is not and still functions, pull the cluster out to check the bulbs.

Charging: sounds like you need a new alternator. If you're mechanically inclined, you can pull the old alternator out and inspect the brushes and regulator. If not, just replacing the whole thing will very likely cure the problem.

The clock buttton also acts a dimmer for the interior lights as well as the dash. Try turning and see if the lights come on. If it does not work the you need a new one. The instrument cluster has to come out. If the alt is not charging. You might get lucky an replace the voltage regulator. The brushes are probably worn. The trick to getting it bolted in is to tie the brush with small fishing line or dental floss. You'll understand when you try and change it. They are spring loaded and its impossible to get back on with out doing it this way. Also, check the terminal block on the firewall for corrsion near the battery in front. Small black box with two wires. A bad batter will also cause charing issue on this car.

The "Certified Mercedes repair shop" that you chose for help is ethically responsible to give you educated suggestions of your car's condition,providing the fact that you paid for the check-out. If the place did not charge you ,then I recommend a reputable Mercedes Exp. shop be your next step. A professional tech. will confirm the problem to be ignition or fuel related and then troubleshoot the faulty system. Good luck!