Car Stereo Head Unit Wire Harness - the12volt Disclaimer: * All information on this site ( the12volt ) is provided "as is" without any warranty of any kind, either expressed or implied, including but not limited to fitness for a particular use. Any user assumes the entire risk as to the accuracy and use of this information. Please verify all wire colors and diagrams before applying any information. How to Identify Aftermarket Car Stereo Wire Colors - Lifewire The problem is that while harness adapters are fairly inexpensive, and they're available for a wide variety of car and head unit combinations, there really isn't any wiggle room in terms of compatibility. For a head unit wiring harness to work, it needs to be specifically designed for both your vehicle and your new head unit.