How to Identify Aftermarket Car Stereo Wire Colors Aug 14, 2019Using a Head Unit Harness Adapter. Although most aftermarket head units follow the above coloring scheme, and it’s possible to figure out what the OEM wires in your car are all for without a wiring diagram, installing an aftermarket head unit is much easier if you have a harness adapter. 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.