Go to best buy, they will have a Radio Installation Bay.

Have them take the 2 radio keys for a Mercedies and pop your radio out. Once they disconnect the harnesses, they can take the deck over to there wall of wire harness kits, and match it up.

Chances are it is identical to the SLK320, as they wouldn't rewire the harness from the amp to the radio just for a mfr change on the deck.