The automobile wiring harness is an important component that connects various electrical and electronic equipment in the automobile.It transmits electrical signals between power supplies, switches, electrical appliances and electronic equipment.It is known as nerve transmission and blood supply.It is a carrier for electrical signal control of automobiles. . Automobile wiring harness is the main body of the network of automobile circuit. Without wiring harness, there is no automobile circuit. 
In order to facilitate installation and maintenance, and ensure that electrical equipment can work in the worst conditions, the different specifications and different colors of electrical wires used in the electrical equipment of the whole vehicle are reasonably arranged into one, and the wires are bundled with insulating materials Bundle, which is complete and reliable.
Automotive wiring harnesses connect automotive switches, appliances, sensors, power supplies, and all electrical and electronic equipment throughout the engine compartment, cab, and exterior of the car. Due to the use characteristics of the car itself, such as: it must repeatedly experience severe environmental and usage conditions such as severe heat, winter, and bumps, which determines the technical requirements of automotive electrical and electronic equipment, so the technical requirements of automotive wiring harnesses are mainly: Correctness and continuity, resistance to vibration, shock, alternating heat and humidity, high temperature, low temperature, salt spray and industrial solvents. 
1) Correct selection of wire cross-section
The electrical equipment on the car selects the cross-sectional area of the wires used according to the size of the load current. For long-term electrical equipment, 60% of the actual ampacity of the electric wire can be selected; for short-time electrical equipment, 60% -100% of the actual ampacity of the electric wire can be used.
2) Selection of wire color code
For easy identification and repair, the wires in the wiring harness are colored differently.
For the convenience of labeling in the circuit diagram, the colors of the wires are indicated by letters, and the colors they represent are noted in each circuit diagram.