The prewiring is on the right hand side of the trunk (passenger side). You will have to remove some of the trunk lining to access the cable. Once you have then panel pulled back, look for a connector (if I recall, it looks like a "Parallel" port that you'd normally plug a printer cable in to). I am sure you will need an adaptor which I believe (?) costs about $50. And mounts?
Good luck and keep us updated.
2006 E350 w/ 155k miles (Daily Driver)
1993 300E 3.2L Sedan w/ close to about 300k miles
2003 E500 Brilliant Silver (Had 217k miles when totalled!)
1989 300E with 289,000 miles (had for <1 yr while in HI)
03 CLK 500 cabrio (Mom's)
2006 C230k (Dad's)
1999 S420 (Mom's/Dad's)
2000 C230k Sport sedans
2001 CLK320 Cabrio (Mom's)
1995 C280 My First Mercedes-Benz... (155k miles. EXCEPTIONAL AUTOMOBILE. Was Very hard to let go of!)