The wire harness is the product reflection of the electrical schematic diagram. It is the carrier for the transmission or exchange of the power signal or data signal of the electrical system to realize the functions of electrical components and meet the real-time control of vehicle driving safety, reliability and entertainment. The wire occupies an extremely important position in the automotive wiring harness and the vehicle electrical system. Ideally, the connections between wires, terminals, and electrical appliances should be carriers of zero potential and zero impedance. Due to the physical properties of the connections, the environmental properties and the properties of the materials, there is always a certain voltage drop in the automotive electrical system. In general, the voltage drop on the line should not exceed 3% of the circuit voltage.