Painless Wire Harness - Easy to Install Wiring Products As part of the Painless Performance commitment to making easy-to-install wiring products, each kit is clearly labeled and comes with a full-color instruction book. Look through the products below and you’re sure to find a quality wire harness to fit your Jeep , hot rod or street legal racing car. Wiring Harness - Painless Engine Wiring Harness | JCWhitney This is where a wiring harness comes in. This particular component is basically an assembly of organized wires that connects your car's components and accessories to a power source. With a damaged or faulty wire harness, your car's gadgets and accessories will be practically useless.