A modern car runs on wiring. The vehicle may look mechanical from the outside, but underneath, it’s a network of power lines and signal paths feeding dozens to hundreds of modules—engine control, lighting, braking sensors, safety systems, infotainment, and, in EVs, high-voltage power distribution. When a wiring harness in car fails, the symptom usually shows up somewhere else: a warning light, a sensor fault, a control module that “sometimes works.” That is why harness issues are expensive—diagnosis often takes longer than the repair.