I put this question in the "08 GPS connector questions" thread, but realize that that thread may be too specific and NOT attract attention to readers to elicit responses.
BTW I do have a 2008 RT, however, this covers more than RTs
So I pose it here....
A friend of mine said his garmin zumo 660LM harness (that came with his GPS) had an end that plugged directly into the BMW GPS plug on his RT.
Plug and play as it were.
Why does everyone say another part is needed? (see other threads).