What Is an Engine Wiring Harness? | Reference wwwrence›Car Parts & MaintenanceAn engine wiring harness is a bundle of wires that distributes electricity throughout a vehicle's engine. It is the network that connects the fuse box to the various components of the engine that require electricity to operate. Modern vehicles have an abundance of accessories and components that are powered by What Is an Engine Harness? | It Still Runs The fuse box protects your vehicle from electrical fire by stopping the current if it is too great. The engine wiring harness first runs from the engine to the fuse box. The fuse box is where the power branches off and goes back into the engine compartment as well as to the rest of your car.