From David Chan: Almost all aftermarket headunits accept a standard antenna cable; years ago I heard it called a Motorola type connector. Your ML320 antenna cable ends in a flat type connector most commonly seen on VW and Audi's. Therefore you will need an antenna adapter to connect the ML320 antenna cable to most aftermarket headunits. This adapter is readily available at most stereo stores for less than $10. Crutchfield has mis-identified the required adapter as one similar to a VW Prassat. Although it will work, it is more complicated and expensive than actually required and might have long term adverse effects on the ML's antenna. This adapter includes a wire which supplies power to the center conductor of the antenna cable. Crutchfield is correct in that the ML has an antenna amplifier requiring power, but power is not supplied to that amplifier via the antenna cable's center conductor but instead via the tan wire in the ML's main radio connector. This wire can be connected to the power antenna wire of most aftermarket headunits to complete the circuit. If power is not supplied to the ML's antenna amplifier, you will have no AM reception and very poor FM reception.
What radios/CD's can be put in the M-Class?