Installing a Head Unit With No Wiring Harness Since there is no factory harness in the picture, you have to options to consider. You can either fashion a new harness for the factory wires that will plug into your head unit harness, or solder your head unit harness directly to the factory wires. 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.