Car wires are also called low-voltage wires are different from ordinary household wires. Automotive wires are made of flexible copper stranded wires, some of which are as thin as hair. Several or even dozens of copper wires are wrapped in plastic insulating tubes, which are soft and not easy to break.

Wires in automobile wiring harnesses with nominal cross-sectional areas of 0.5, 0.75, 1.0, 1.5, 2.0, 2.5, 4.0, 6.0 mm2 (nominal cross-sectional areas commonly used in Japanese cars are 0.5, 0.85, 1.25, 2.0 , 2.5, 4.0, 6.0, etc. square millimeters), each of them has an allowable load current value and is equipped with conductors for electrical equipment of different powers.

In automobile electrical circuits, wires for different purposes are distinguished by different colors to facilitate the installation and maintenance of automobile circuits.

Taking the vehicle wiring harness as an example, the 0.5 gauge wire is suitable for instrument lights, indicator lights, door lights, ceiling lights, etc.; the 0.75 gauge wire is suitable for front and rear small lights, brake lights, etc.; the 1.0 gauge wire is suitable for turn signals, fog lights etc.; 1.5 gauge wire is suitable for headlights, speakers, etc.; main power wires such as generator armature wires, ground wires, etc. require 2.5 to 4 square millimeter wires.

The battery ground wire and power wire are special car wires used separately. Their wire diameters are relatively large, at least more than ten square millimeters. These wires will not be integrated into the main wiring harness.

Due to the particularity of the automotive industry, the manufacturing process of automotive wires is more special than other ordinary wires. To make sure that the wires have a certain mechanical strength, the cross-sectional area of the wires should not be less than 0.5 mm2. Since the starter works for a short period of time, in order to ensure that the starter can emit sufficient power during normal operation, it is required that the voltage drop generated by every 100A of current on the wire cannot exceed 0.1V-0.15V. Therefore, the cross-sectional area of the wire is large. The high-voltage wires of automobiles have extremely high voltage resistance, generally above 15KV, so their cross-sectional area is very small (because the current is very small), about 1.5 mm2, but the thickness of the insulation layer is much thicker than that of lower-voltage wires. They are mostly insulated with rubber.

Automotive wires are low-voltage power supplies with large operating currents and large voltage losses. Excessive voltage loss will affect the normal operation of electrical equipment. Therefore, when selecting the conductor cross-sectional area, it is necessary to ensure that the voltage loss does not exceed a certain value: no more than 0.5V for 12V systems and no more than 1.0V for 24V systems. The actual operating current of the conductor is not allowed to be greater than the allowable carrying capacity of the conductor.