In today's automotive industry, wiring harnesses are constructed in a similar manner for both high-end luxury vehicles and affordable, standard vehicles. The wiring harness primarily consists of wires, connectors, and wrapping tape, forming the core network of the vehicle's electrical circuit. Without the wiring harness, the vehicle's electrical circuit would cease to exist.
Automotive wiring, often referred to as low-voltage wiring, differs from the wiring used in household appliances. Household appliance wiring is mostly single-core copper with a certain degree of rigidity. Automotive wiring, on the other hand, is multi-core copper, flexible wire, some as thin as a human hair. These flexible wires are encased in plastic insulation (polyvinyl chloride), making them flexible and resistant to breakage.
The wires in automotive wiring harnesses come in a variety of gauges, with common sizes including 0.5, 0.75, 1.0, 1.5, 2.0, 2.5, 4.0, and 6.0 square millimeters. Each gauge has a specific load current rating to accommodate the needs of electrical equipment of varying power. For example, 0.5 square millimeter wire is often used for low-power devices like instrument lights and indicator lights; while main power lines, such as generator armature wires, require 2.5 to 4 square millimeter wire.
Of course, this is only a typical wiring harness configuration. In actual applications, wire gauge selection also depends on the maximum current of the load. For example, critical lines like the battery ground wire and the positive power line are routed separately using specialized automotive wiring, often with wire diameters exceeding 10 square millimeters. These "giant" wires are not incorporated into the main wiring harness.
Before wiring harnesses are laid out, a wiring harness diagram is usually drawn in advance. Unlike circuit schematics, wiring harness diagrams require detailed consideration of the size, shape, and spacing of each electrical component, and accurately reflect the connections between them.
The wiring harness manufacturing process begins with a technician creating a wiring harness layout based on the wiring harness diagram. Workers then cut and arrange the wires according to the layout's specifications. A vehicle's wiring harness is typically divided into several sections, including the engine (involving the ignition, electronic fuel injection, generator, and starting systems), instrumentation, lighting, air conditioning, and auxiliary electrical systems. These include both main and branch harnesses. These harnesses are arranged like the trunk and branches of a tree, with the instrument panel often serving as the core, extending forward and backward. For reasons of length and ease of assembly, some vehicles' wiring harnesses are further divided into a front harness (covering the instrumentation, engine, headlight assembly, air conditioning, and battery), a rear harness (including the taillight assembly, license plate, and trunk light), and a roof harness (serving the doors, dome lights, and speakers). Each harness end is clearly marked with numbers and letters to indicate the connection, simplifying repair or replacement. Wires are also categorized as single-color or two-color, with color selection typically based on manufacturer-specified standards.
Wire harnesses are primarily wrapped with woven wire or plastic tape. However, for safety reasons and ease of processing and maintenance, woven wire wrapping has been gradually phased out in favor of adhesive plastic tape. Connectors or lugs are primarily used to connect wiring harnesses to each other and to electrical components. These connectors are made of plastic and consist of a plug and a socket.
Furthermore, with the increasing functionality of automobiles, the widespread use of electronic control technology, and the increasing number of electrical components, wiring harness manufacturing faces new challenges. Traditional wiring harnesses are no longer able to cope with this growth trend. Therefore, advanced automotive manufacturing technology has begun to incorporate CAN bus configurations and multiplexed transmission systems. This system significantly reduces the number of wires and connectors, making the wiring process simpler and more efficient.
