You would need to look at wiring diagrams for BOTH the CAR and the RADIO!

Generally different model year cars will use different wire colors. So it helps to also say what year and model car you have if asking questions.

Different radios have different features as well as using various wire colors for this and that, so helpful to include a link to the wiring diagrams of your radio.

My radio (upon looking at the wiring diagrams and reading the instructions) had a connection for the light dimmer. Some radios do not.

Note some Mercedes have an alarm wire. And an automatic antenna wire.

Also note that some Mercedes wiring diagrams have the wire color abbreviations in German! Here is a translation...

BL blau blue
BR braun brown
GE gelb yellow
GR grau gray
GN grun green
RT rot red
SW schwartz black
WS weiss white
VI violett violet