A SAM is a "System Activation Module". What it means, in laymans terms, is a computer that controls various functions of the car. Usually if you think of a computer in a car, you think of like the engine control unit, something that has a definite job to do, like run the engine. These SAM's have various "little" tasks to do, not just one "big" job. Some of them may run a few different lights, and maybe work part of the door locks, and pop the trunk lid for example.
But here's my impression:
First, usually the dash on a 203 chassis will not only tell you that a light is inop, it will also usually give you some indication of WHICH light is out. Aren't you getting some type of clue as to which one it is? It may be rather cryptic in nature, like "LR Tail" or something like that.
Also, this is really trick, but it also has whats called "substitute lighting". What it may do is for example if the Left tail light is out, it will switch off BOTH of the "normal" tail light bulbs and instead use BOTh of the brake light bulbs at a reduced brightness to mimic a pair of tail lights. They won't be in the "correct" place that the tail lights are supposed to be in, but it will look "normal" to anyone not familiar with the tail lights on your car. So study that a little. If the tail lights are at the top position of the rear lenses, that's not right, it's using substitute lighting.
There were just a real rash od bulb outtages on 203 chassis for the first year or two. On the tail lights they came out with an adapter harness for the tail lights, your dealer should be aware of this, there is a bulletin on it.
Also on the FRONT park/turn signals, there is also a kit which should be installed which modifies the harness, there is also a bulletin on this problem as well for the earlier C Class cars.
BOTH of these bulletins deal with inop lights, the one for the rear deals with burning out bulbs rapidly, and the front kit just deals with the bulbs not working due to a bad ground connection.
They are both quite common occurances on the 203 chassis C Class.

Gilly

ps IC is instrument cluster