Factory Fit® OEM Restoration Wiring Harnesses and Parts Wiring harnesses and accessories are installed as a direct replacement to the original factory wiring – no guesswork. We call it a “plug and play” experience. We call it a “plug and play” experience.Classic Update Series · Download Catalog · Truck Exact OEM Reproduction Wiring Harnesses for Classic Our Original Design Series™ wiring harnesses are manufactured exactly as the wiring was made when your vehicle left the factory. These harnesses are made to the exact O.E.M. (original equipment manufacturer) specifications, using the original factory blueprints, and are factory-correct in every way.