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Type, failure mode and inspection method of automobile harness
Time:2022-01-06 Read: 1293

Car harness is the main network of car circuit. Without harness, there is no car circuit. In the automobile harness, the important component is the wire.

Conductors deliver current to electronic components, and most of them are made of copper. The cross-sectional area of the wire used in the automobile determines the allowable current.

Each circuit in the car has its own circuit number, and each wire has its own color. The wire can be monochromatic or striped.

Harness type

1. Ordinary conductor

Ordinary conductors are usually made of multi-stranded fine copper wire. The multi-strand form has better bending resistance and is not easy to break due to repeated vibration.

The common conductor is composed of copper core and external insulation material. PVC material is usually used as insulating material, with the following advantages:

① Will not melt under high current

② No open fire

③ Light weight

2. Shielded conductor

The main function of shielded wire is to prevent electromagnetic interference. If the signal harness is close to a high current or high voltage harness or component, the signal wire will be subject to electromagnetic interference, resulting in signal misalignment. The outer layer of the shielding conductor is grounded with aluminum foil or mesh harness. Electromagnetic interference is removed by direct grounding.

Factors affecting wire resistance

The resistance of wire is very important for current transmission. The factors affecting the resistance of wire are as follows:

1. Temperature

The effect of temperature on various materials is different. For example, the resistance of copper and steel increases with the increase of temperature. For some materials, the resistance of materials will decrease with the increase of temperature. When measuring the resistance of wire, we must disconnect the measured wire from the circuit.

2. Sectional area

The larger the cross-sectional area of the wire, the more electrons will pass through at the same time. The thinner the wire, the more difficult the current is to pass through, and the greater the wire resistance. The resistance decreases with the increase of wire diameter. When replacing the harness, the harness with the same wire diameter must be used. If a thinner wire harness is used, the resistance of the wire will increase, the power consumed by the wire will increase, and the wire harness will overheat or melt.

3. Length

As the length of the wire increases, the resistance increases because electrons must pass through more atoms. The electrons passing through the shorter wire meet fewer atoms, so the resistance is smaller.

4. Rust

Rust in the circuit will also affect the resistance, which will increase after corrosion.

Wire inspection

For wire inspection, it is necessary to use the resistance of a multimeter to measure the resistance of the wire. The specific operation method is as follows: First, disconnect the measured wire from the circuit; Then, select the appropriate range of the multimeter. The multimeter needle contacts the wire. If the resistance exceeds the standard value, check whether the wire grounding and plug are in the virtual connection state.


Connector, also known as plug. The plug in the automobile circuit is a frequently used component in the automobile circuit. Its function is to connect different wires in the circuit together, so that the current can flow, so that the circuit can achieve the predetermined function.

1. Structure of connector

Car plugs are mainly composed of pins, shells and accessories.

2. Classification of connectors

Classification by connecting parts:

There are two types of plugs: wire and wire plug, wire and component plug.

Wire and wire plug refers to that both ends of the plug are connected with wire harness, and the plug plays a role of connection.

Wire and component plug refer to the plug that the harness connects to some components.

Classification by plug structure:

Plug can be divided into male plug and female plug according to its structural characteristics. Male plug is mainly pin. The female plug is mainly spring plate.

3. Failure mode of connector

Common plug failure forms include dirty plug, pin falling off, loose plug, etc.

(1) The plug is dirty. Dirty or corroded plug can easily cause short circuit between plug pins.

(2) The pin falls off. The pin clip on the plug housing is damaged, which is easy to cause the pin of the plug to fall off. After the pin falls off, the plug has poor contact.

(3) The plug is loose. If the fixing clip on the plug housing is damaged, it is easy to loosen the plug, which will affect the operation of electrical components.

4. Inspection of connector

The plug is mainly checked in the following aspects:

(1) Visual inspection

Check the oxidation, which may cause poor connection of the internal terminal of the plug;

Check whether the pins and terminals are damaged;

Check whether the connector is inserted correctly;

Check whether the wire is correctly connected to the pin or terminal;

Check the pins and terminals carefully.

(2) Plug measurement

Connect a multimeter at both ends of the wire and measure the resistance; If the plug contacts well and there is no open circuit, the multimeter reading should be around 0.

(3) Check whether the plug pin is loose

Check whether the wire pin on the plug is loose. If it is found, repair it in time.

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Shenzhen WENJIAN Electronics Co., Ltd

Address: 4th floor, No. 6, Shangliao Puyuwei Road, Shajing Street, Bao'an District, Shenzhen, Guangdong Province
Tel: 0755-82598337
Fax: 0755-27281825
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Luo Sheng 15007550148

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