You can add an auto dimming rear view mirror to your "older" C class (or any other MB). The mirror comes with a 5-pins plug that is connected to the front courtesy light (in the newer models that is). Your car does not have a suitable courtesy light and therefore you need to create your own connecting plug. The mirror has a gray/blue-line wire for power (either power from interior (dash) lights or ignition-switch(ed) power), a brown wire for the ground and three pink wires with a different color line. These three wires are for connecting the auto dimming side mirrors and connecting to the door contacts/reverse lights (to prevent the mirror from dimming when the door is opened or when you are reversing), but these are not necessary for an operating auto dimming mirror.
I have installed one in my 1993 C250D as well.
with a minor 600+k