Introduction to the composition of automotive wiring harness and function

Automotive wiring harness is the network backbone of a vehicle's electrical circuit, connecting the electrical and electronic components of a car and enabling their functionality. Without a wiring harness, automotive circuits would not exist. Currently, whether it's a high-end luxury car or an economy car, the form of wiring harness assembly is essentially the same, consisting of wires, connectors, and wrapping tape. It not only ensures the transmission of electrical signals but also guarantees the reliability of circuit connections, supplying the specified current to electronic components, preventing electromagnetic interference to surrounding circuits, and eliminating electrical short circuits.

What is a wiring harness?

An automotive wiring harness is often likened to the nervous system of a car. It serves as the network backbone of a vehicle's electrical circuit, and without a wiring harness, automotive circuits would not exist. A wiring harness, literally a bundle of wires, defines the usage environment of the harness, which is installed on the car, as shown in the diagram below:

The wiring harness spans throughout the entire vehicle, connecting various electrical devices and serving as a medium for power supply and signal transmission. The wiring harness is often likened to the nervous system of a car and serves as the network backbone of the vehicle's electrical circuit.

Functions and roles of a wiring harness

The wiring harness is an indispensable system-level component in a vehicle. Its role is to provide and distribute power to various systems in the vehicle while serving as a medium for signal transmission between different components.

To put it simply, for electrical components in a car, such as headlights to receive power for illumination, they need to be connected to the battery or generator through a wiring harness, forming a power circuit. Additionally, for the headlights to illuminate, the body control module (BCM) needs to recognize the driver's intent to turn on the lighting switch, and the signal interaction between the combination switch and BCM also requires the use of a wiring harness.

Components of an automotive wiring harness

The components of a low-voltage wiring harness are extensive and include cables, connectors, terminals, fuse boxes, relays, fuses, plastic brackets, metal brackets, PVC insulation tubes, corrugated tubes, heat shrink tubes, seals, rubber covers, tapes, cable ties, protective covers, bolts, and more.

An automotive wiring harness is composed of wires, connectors, harness wrapping materials, harness fasteners (clips, rubber components, harness brackets, etc.), and harness accessories.

1. Wires

Wires, also known as conductors, are the main components of a wiring harness. They are the core part of the harness and primarily carry the current required for the loads. The important parameter of a wire is its current-carrying capacity, which is influenced by factors such as wire diameter (cross-sectional area of the conductor), wire length, conductor resistivity, and ambient temperature.

1. Connectors

Connectors, also known as plugs, are indispensable components for connecting the wiring harness to other electrical devices. They are divided into harness connectors and device connectors.

We often hear about male connectors (referred to as male terminals) and female connectors (referred to as female terminals). The connector that houses male terminals is called a male connector, while the connector that houses female terminals is called a female connector. The connectors on the harness end are usually female connectors.

For a wiring harness, connectors are relatively precise components. To ensure the connection performance between the wiring harness assembly and electrical devices, it is generally required to use a complete set of connectors, meaning selecting connectors of the same manufacturer and series.

Connectors can be broadly classified into two categories: waterproof and non-waterproof. During the design phase, different width pins are selected based on the current they need to carry, and chambers are formed in the connector to accommodate the various pins, creating a housing that can hold multiple pins.

Connector Position Assurance (CPA) is a secondary locking mechanism for the connector housing. Its purpose is to ensure that the housing and electrical interface remain securely locked after initial assembly. Due to the specific nature of its function, CPA design must consider the operator's usability and visibility. Therefore, the CPA must be an independent mechanism on the housing and have distinctive color markings.

There are two types of waterproof sealing rings: one is used for sealing between housing components, and the other is used to seal terminal leads.

Terminal Position Assurance (TPA) is a secondary locking structure for terminals. Not all terminals require TPA. Volkswagen, for instance, mandates the use of TPA for terminals with a width equal to or less than 2.8mm. To facilitate installation by wire harness workers, TPAs must be easily identifiable by color and have a clear tactile feel during assembly. To prevent TPAs from automatically locking during transportation to the wire harness factory, an anti-locking mechanism is required on the TPA.

1. Wire Harness Bundling Materials

The main function of wire harness bundling materials is to protect the wire harness. Depending on the material used, there are various types of bundling materials, including corrugated tubes, PVC tapes, fabric-based tapes, velvet tapes, sponge tapes, and aluminum foil tapes.

Due to the different material properties, each type of bundling material has its own application conditions and methods on the wire harness assembly. Therefore, when selecting the appropriate material, it is important to consider the specific operating environment of the wire harness and its requirements for wear resistance and heat resistance.

1. Wire Harness Fixtures

Unlike other components in a car, wire harnesses are flexible and cannot be presented in a predetermined form. Therefore, additional components are required to secure and guide the wire harness along the designated routing paths in the vehicle. These additional components are called wire harness fixtures, and they serve the purpose of securing and constraining the wire harness layout.

Wire harness fixtures include cable ties, clips, rubber sleeves, wire harness brackets, etc. Depending on the installation environment of the wire harness, such as available space, temperature requirements, and waterproofing needs, the shape and material of each type of wire harness fixture may vary. Nevertheless, there is a trend towards standardization in wire harness fixtures, making it easier to achieve component selection in wire harness platform design.

1. Wire Harness Accessories

Wire harness accessories refer to smaller products used in the wire harness assembly, such as product labels and fuse holders.

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