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 CHAD2C ISO Non Amplified AUDI A3 1996-2003 (CONCERT / SYMPHONY) AUDI A4 1995-2004 (CHORUS / BLAUPUNKT) AUDI A6 1997-2004 (MATSUSHITA / GRUNDIG) AUDI A8 1994-2002 (NO MK II VERSIONS) AUDI TT 1999 (NO 4:3 NAVIGATION!) MODELS WITHOUT CAN-BUS