This is the wiring loom you need to add the 3.5mm auxiliary input to W169 A, W245 B, W164 ML, R251 R class, and Vito/Sprinter.

It is used on the W203/W209 if there is no intermediate connector in the footwell.

You need to drill a 19mm hole in the glovebox (The W164 ML/GL and R251 R class already have a hole with a cover on it) in the glovebox on the side near the stereo. The lead then clips into the hole and connects into the multiway connector on the back of the COMAND or Audio-20 system.