Helga is a 1996 C220 whose Warning Light on the dash indicating that a bulb is out started to come on and off for no particular reason, or at least so it seems: no light on the entire car is off when this light comes on. To further complicate things, the Check Engine Light also comes on intermittently, but not when the warning light comes on. I took Helga to the car doc (I've been avoidubng the Benz dealer for noe!) and they couldn't figure things out. Oh, did I mention that opening the trunk and slamming it shut took care of the problem for one afternoon. I unfortunately cannot recreate the conditions of this last experiment which could have been an easy fix. I'm totally baffled!!!

 

Slamming the trunk is probably still key to the fix, if the light problem went away for a while. All your rear lights bulbs and also front corner lights, need to be checked for the right type, their connections, wiring connects to the bulb connectors, etc. From experience, I know MB cars are sensitive to these front and rear light bulbs' connectivity and integrity. Check engine light on should be separate issue(s) and needs a diagnostic scan. Try the bulbs checking first, then have the computer modules error codes scanned and let us know.

 

Bill is spot on.
However if all bulbs and connections are fine it MIGHT be early signs of the PSE playing up.

CEL coming on is likely an entirely different problem but don't worry till it comes on and stays on.

The PSE controls the door locks, security system AND THE BULB WARNING system. PSE problems occur due to water/moisture ingress into the white multi connector on the PSE.
Not sure exactly where in the rear the PSE is located on your car. Lots of yellow pneumatic tubes coming out of it. Look for any signs of corrosion (blue deposit) or worse still moisture.

Stuart