@beckham388 Do you have a part number for that cable? Mine is missing.
[Edit] Wait, that may not be what I'm looking for. I think there is one with a USB connector and an audio jack.

 

Mercedes media interface cable. There are a lot of choices on Amazon and Aliexpress.

 

 

Thanks. What does the other end look like?

 

Apple iPhone Lighting connector.

 

I recently installed a Roadtop black model in my wife's 2013. Her vehicle has the MMI input in the armrest and even though the MMI to aux cable was supplied with the kit it was not actually required.

Once AUX was enabled in the engineering menu and the car was left to sleep for 10-15 mins so the setting actually took.. all that was left to do was connect the 2 ground wires on the harness and sound was good to go.

It took a bunch of trial and error to get to the ground wire solution... I fought with it for over 2 hours playing with engineering menu options and doing various reboots and still not getting any audio. I was preparing to pull the center console out to run an AUX cable to the armrest before I finally tried the ground wires... been flawless ever since.