Steering Wheel control Primary harness adapters convert the commands from your car's steering wheel controls to a code that an aftermarket radio can recognize. A patch lead is also requires for SWC type systems based on the brand of head unit you have. for more details check out our you tube video. http://aerpro.com/video/control_harness_installation CHBM7C Non iDrive Vehicles BMW 1ER 2004 UP (E87) BMW 3ER 2006 UP BMW 5ER 2005 UP BMW 6ER 2005 UP BMW MINI 2006 UP BMW X1 (E84) 2009 UP BMW Z4 (E89) (WITH METAL ROOF) ALL CARS WITH INTERIOR CAN-BUS (WITH 40 PIN) ONLY FOR CARS WITHOUT IDRIVE HEAD UNIT SUPPORTS SPEED / REVERSE