Fitting a CD changer in the glovebox on the A and B class is fully described in my document COMAND APS Retrofit document

Fitting the CD changer in the glovebox in a facelifted W203 C & W209 CLK is almost identical but different parts are needed, and the dismantling of the glovebox and dash is different - but the above document will help you with what the wiring looks like.

Fitting a CD changer to the ML, GL and R class is described in my ML CD changer retrofit document.