Types and selection methods of automobile wiring harness terminals

The harness terminal is a conductive element that can form a circuit with the corresponding conductive element. The terminal includes two kinds of pins and sockets, which play the role of electrical connection. The materials used are good conductors such as copper and its alloys. The surface is plated with silver, gold or tin to improve corrosion resistance and oxidation resistance. and anti-rust.


1. Terminal type

Terminals can be divided into sheet series, cylindrical series and wire joint series according to their shape.
1) The chip series terminals are made of H65Y or H70Y material, and the material thickness is 0.3 to 0.5.
2) The cylindrical series terminals are made of H65Y or Qsn6.5-0.1 material, and the material thickness is 0.3 to 0.4.
3) Wire connector series terminals are divided into three types: U-shaped, fork-shaped and hole-shaped.
① The U-shaped terminal is made of H62Y2, H65Y, H68Y or Qsn6.5-0.1 material, with a thickness of 0.4 to 0.6;
②The fork terminal is also called the Y-type terminal. The Y-type terminal is made of H62Y2 material, with a material thickness of 0.4 to 0.6, and part of the surface is nickel-plated, with good electrical conductivity;
③ Hole terminals generally use H65Y and H65Y2 as the base material, and the material thickness is 0.5 to 1.0.


2. Terminal selection principle

Different plated terminals should be selected according to different connectors and different needs. For equipment with high performance requirements, such as terminals for airbags, ABS, ECU, etc., gold-plated parts should be preferred to ensure safety and reliability, but due to cost considerations, partial gold-plated treatment can be selected under the premise of meeting performance requirements.

The specific selection principles are:
① Ensure that the terminals are reasonably matched with the selected connectors.
②Select the appropriate terminal for the wire diameter of the crimped wire.
③For the single-hole waterproof connector, select the terminal whose tail can be crimped to the waterproof plug.
④ Ensure the reliability of the connection. When selecting terminals, ensure good contact with electrical devices and plug-ins, so as to minimize contact resistance and improve reliability. For example, surface contact is better than point contact, and pinhole type is better than leaf spring type. In the design, it is preferable to use a connector with a double spring compression structure (very low contact resistance).
⑤ Impedance matching. Some signals have impedance matching requirements, especially RF signals, which have stricter impedance matching requirements. When the impedance is not matched, signal reflection will be caused, thereby affecting signal transmission. Therefore, when selecting a terminal, be sure to select a terminal with matching impedance.

Factors that affect wire resistance are as follows

1. Temperature

The effect of temperature on various materials is different. For example, the electrical resistance of copper and steel increases with temperature. For some materials, the resistance of the material decreases with temperature. When conducting wire resistance measurements, we need to disconnect the wire under test from the circuit.

2. Cross-sectional area

The larger the cross-sectional area of ​​the wire, the more electrons can pass through in the same amount of time. The thinner the wire, the harder it is for current to pass and the greater the resistance of the wire. The resistance decreases as the diameter of the wire increases. When replacing a wire harness, use a wire harness of the same wire diameter. If a thinner wire harness is used, the resistance of the wire increases, the resistance increases, the power dissipated by the wire increases, and the wire harness overheats or melts.

3. Length

As the length of the wire increases, the resistance increases because the electrons have to pass through more atoms. Electrons traveling through shorter wires encounter fewer atoms and therefore have less resistance.

4. Rust

Corrosion in the circuit also affects resistance, which increases after rusting.

Harness plugs are rarely seen in life, and are not used much in real life, but in the auto repair industry, wire harness plugs are a basic common plug-in tool, called a relay station for line transfer, which can be connected to a variety of ports , to achieve line circulation.

Factors Affecting Terminal Crimp Performance (Part 2)

1. The material of the conductor

With the same wire diameter, the current-carrying capacity of the copper wire is larger than that of the aluminum wire, but the weight of the copper wire is also relatively large. Generally, the conductor is bare copper or bare aluminum, but there may be a coating on the outside of the conductor as required. The common coating materials are tin and silver. In a sulfur-containing environment, the coating of the wire should be tinned. In the case of high requirements on the contact resistance of the wire, silver plating can be used to reduce the contact resistance.

2. Insulation material

The higher the electrical resistance and resistivity of the insulation, the better. In the case of high frequency and high voltage, insulating materials with small dielectric loss tangent should be used.

3. Conductor current carrying capacity

The selection of conductors is often based on the current carrying capacity of the target. When selecting a wire, the current carrying capacity of the wire is usually the first factor.

Factors Affecting Terminal Crimp Performance (Part 1)

1. Terminal material

The following characteristics are important to consider when selecting terminal materials:

①The mechanical properties of the material. Strength, ductility, yield strength, hardness, etc.;

②The electrical conductivity and thermal conductivity of the material. There is a proportional relationship between the electrical conductivity and the thermal conductivity. The electrical conductivity is related to the electrical conductivity of the terminal and the size of its own resistance.

③ Stress relaxation resistance. The terminal is divided into a crimping part and a connecting part. The elastic-plastic deformation of the crimping part causes stress between the terminal and the wire. If the stress relaxes, the contact between the terminal and the wire will become unstable. If the connection part of the terminal is To communicate through plug deformation, stress relaxation and fatigue issues need to be considered.

2. Terminal plating

Electroplating on the terminal surface is a process method to solve the metal oxidation and corrosion of the terminal surface, strengthen the terminal conductivity and reduce the contact resistance. The most commonly used terminal plating is tin plating, in addition to gold plating, silver and nickel or chromium.

Gold itself has high chemical stability, strong corrosion resistance, high temperature resistance, easy welding, strong electrical conductivity, and certain wear resistance. However, because the metal is used for cathodic coating, the price is also relatively expensive. Due to the thin gold coating and insufficient process technology, the coating has pores in actual production, which will cause microporous corrosion, which affects the protective performance. Therefore, it is often used in terminals. connection part to reduce the contact resistance of the connection.

Silver itself also has high chemical stability, is not easy to corrode in the air, has good welding performance, and has good electrical and thermal conductivity. However, its disadvantage is that it will be halogenated or sulfided when exposed to the air containing halides and sulfides, the surface of the silver coating will be discolored, and the electrical conductivity will decrease. In addition, microporous corrosion will also occur in case of moisture, so it is often used in the terminal connection part like gold to reduce the contact resistance of the connection.

Tin has good chemical stability, high ductility, and is difficult to change color in the atmosphere. And because the tin plating layer is relatively soft, it can improve the running-in effect on the sliding parts of the machine. Therefore, tin plating can improve solderability and prevent nitridation. It is commonly used in electronic products and is a common terminal plating process.

In addition, there are nickel plating and chromium plating. When the thickness of nickel plating is less than 25 microns, there are more pores. In addition, the solderability of nickel plating is deteriorated due to passivation. The hardness, wear resistance and heat resistance of chromium plating are good. Chrome plating is mainly used for decorative plating and functional purposes.

It can be seen that there are many kinds of plating layers of terminals. The plating layer of the crimping part of the terminal is generally tin-plated, and the plating layer of the connecting part of the plug-in terminal is gold-plated, silver-plated, and multi-plated. required coating.

3. Influence of terminal design parameters

The design parameters of the terminal generally refer to the parameters of the crimping part, mainly referring to the inner and outer diameter of the terminal, the engagement length, and the depth, number and arrangement of the dents.

①Internal and external diameters.
The inner and outer diameter of the terminal determines the thickness of the terminal. The smaller the bending radius, the greater the relative elongation of the outer metal. When the relative elongation of the outer metal reaches the ultimate elongation of the material, that is, the bending radius reaches the minimum value, the material will have a bending crack. The selection of terminal thickness needs to be determined according to the wire diameter of the crimped wire.

② Mesh length.

The influence of the engagement length on the pull-off force of the terminal: the longer the engagement length, the larger the contact area between the terminal and the wire, and the stronger the contact between the terminal and the wire under the same crimping degree, the greater the pull-off force.

The influence of meshing length on the contact resistance of the terminal: the longer the meshing length, the larger the contact area between the terminal and the wire, and the smaller the contact resistance of the crimped terminal under the same crimping degree.

③ Depth, number and arrangement of dents

Indentations are generally present on the inner surface of the crimp portion of the terminal as a way to increase the mechanical and electrical properties of the terminal. The depth, number and arrangement of the dimples have different effects on the performance of the terminals.

Introduction of high voltage connectors

High-voltage connectors refer to connectors with AC voltages above 1000V or DC voltages above 1500V, mainly used in vehicles, charging facilities, industrial equipment, medical equipment, etc.

Electric vehicles have very strict requirements on connector performance. High insertion and removal times, current carrying capacity, CTI value, flame retardant performance and vibration resistance are the key factors that enterprises need to consider in product development, and the power demand of electric drive units for new energy vehicles is increasing. Higher requirements are placed on working current and voltage. The traditional connection voltage is around 14V, while the voltage of electric vehicle high-voltage connectors reaches 400-600V.

At the same time, the sealing performance of high-pressure connectors is generally required to be at least IP67, and even IP6K9K is required when selecting models in some special occasions of automobiles to ensure that they can meet the requirements even during high-pressure washing.

Since new energy vehicles use a lot of power electronic equipment, the electromagnetic field generated by high voltage and large current will cause electromagnetic interference to other communication equipment. The whole vehicle and its parts must have anti-interference and anti-radiation capabilities.

When designing a high-voltage electrical connection system, it is required that the connector has a 360° shield and is effectively connected to the cable shield, covering the entire length of the connector to ensure adequate shielding function and minimize the resistance between the shields at the interface . The shield connection contact resistance is less than 10mΩ during the lifetime.

Therefore, the high-voltage connectors of new energy vehicles need to use new materials that are resistant to high temperature and high pressure. At the same time, they are also higher than traditional automotive connectors in terms of sealing, shielding and waterproofing, and have higher requirements for flame retardancy and CTI value, so the cost is higher than that of general industrial connectors. At present, most of the high-voltage connectors on the market use high-performance PBT, PA, etc.

The standard of Cat8 network cable

In the field of ethernet communication, when it comes to ethernet cables, it is often mentioned that the Cat5e ethernet cables, the Cat6 ethernet cables and the seven types of ethernet cables are mentioned. However, in recent years, Cat8 cables have begun to be mentioned more, so what is the difference between Cat8 ethernet cables and previous cables?

Cat8 ethernet cable is the latest generation of double-shielded (SFTP) ethernet jumper. It has two signal pairs, which can support 2000MHz bandwidth, and the transmission rate is as high as 40Gb/s, but its maximum transmission distance is only 30m, so it is generally used. Connecting servers, switches, patch panels and other equipment in short-distance data centers.
At present, the common ethernet cables on the market are Cat5e ethernet cables, Cat6 ethernet cables, Cat6e ethernet cables, Cat7 ethernet cables and Cat7e cables. Cat8 CAT8 ethernet cable is the same as Cat7/Cat7e ethernet cable, it is a shielded twisted pair cable, which can be used in data centers, high-speed and bandwidth-intensive places, although the transmission distance of Cat8 ethernet cable is not as good as that of Cat7/Cat7e ethernet cable It is far, but its speed and frequency are much higher than those of Cat7/Cat7e ethernet cables. There is a big difference between the Cat8 ethernet cable, the Cat5e ethernet cable, the Cat6 ethernet cable, which is mainly reflected in the speed, frequency, transmission distance and application.

The relevant standards of Cat8 ethernet cables were officially released by the TIA TR-43 Committee in 2016, as follows:
1. Compliant with the IEEE 802.3bq 25G/40GBASE-T standard, which specifies the minimum transmission rate of Cat8 ethernet cables, which can support 25 Gbps and 40 Gbps network wiring.
2. Complies with ANSI/TIA-568-C.2-1 standard, which specifies the channel and permanent link of Cat8 ethernet cable, and includes the limitation of resistance unbalance, TCL and ELTCTL.
3. Comply with ANSI/TIA-1152-A standard, which specifies the measurement and accuracy requirements of Cat8 ethernet cable field tester.
4. Comply with ISO/IEC-11801 standard, which specifies the channel and permanent link of I/II Cat8 ethernet cable.

How to Choose a Low Frequency Connector (Part 4)

-Environmental Parameters-

Ambient temperature

The metal material and insulating material of the connector determine the working ambient temperature of the connector. High temperature will damage the edge material, causing the insulation resistance and withstand voltage performance to decrease; for metals, high temperature can make the contact pair lose elasticity, accelerate oxidation and cause coating deterioration. The usual ambient temperature is -55~100°C, which may be higher in special occasions.


Relative humidity greater than 80% is the main cause of electrical breakdown. Humid environment causes the absorption and diffusion of water vapor on the surface of the insulator, which is easy to reduce the insulation resistance to below MΩ level. Long-term exposure to high humidity environment will cause physical deformation, decomposition and escape of products, resulting in breathing effect and electrolysis and corrosion. and cracks. Especially for connectors outside the equipment, environmental conditions such as moisture, water infiltration and pollution are often considered. In this case, sealed connectors should be selected. For water-tight and dust-tight connectors, the enclosure protection level of GB4208 is generally used.

Temperature abrupt change

The humidity shock test is to simulate the actual use situation of using connector equipment to switch from a cold environment to a warm environment, or to simulate the rapid change of the ambient temperature of space vehicles and probes. Abrupt temperature changes may crack or delaminate the insulating material.

Atmospheric pressure

At high altitudes where the air is thin, the plastic emits gas to contaminate the contact pair, which increases the tendency of corona generation, reduces the voltage resistance, and causes the circuit to short-circuit. When the altitude reaches a certain value, the performance of the plastic deteriorates. Therefore, when using unsealed connectors at high altitudes, they must be derated.

Corrosive environment

According to the different corrosive environment of the connector, choose the connector with the corresponding metal, plastic and coating structure, such as the connector used in the salt spray environment, if there is no anti-corrosion metal surface, the performance will deteriorate rapidly. Connectors with silver-plated contact pairs should not be used in environments containing considerable concentrations of SO2. Mold is also a significant problem in hot flash areas. 5. Termination method Termination method refers to the connection method between the contact pair of the connector and the wire or cable. Reasonable selection of termination methods and correct use of termination technology are also an important aspect of using and selecting connectors.

How to Choose a Low Frequency Connector (Part 3)

-Mechanical Parameters-

contact pressure

In most structures, direct measurement of contact pressure is rather difficult. Therefore, the contact pressure is often measured indirectly by the single-foot separation force. For a circular pinhole contact pair, a standard pin with a specified weight is usually used to test the ability of the female contact to hold the weight. Generally, the diameter of the standard pin is -5μm, the lower limit of the diameter of the male contact. The total separation force is generally twice the sum of the upper and lower lines of the single foot separation force. When the total separation force exceeds 50N, it is quite difficult to insert and pull out manually. Of course, for some test equipment or occasions with special requirements, zero insertion force connectors, automatic detachment connectors, etc. can be selected.

Mechanical life

The mechanical life of the connector refers to the insertion and removal life, which is usually specified as 500 to 5000 times. When reaching the specified mechanical life, the contact resistance, insulation resistance and withstand voltage of the connector should not exceed the specified values. Strictly speaking, the current mechanical life is a vague concept. The mechanical life should have a certain relationship with time. Obviously, the situation is different when it is used up 500 times in 10 years and 500 times in 1 year. It’s just that there is no more economical and scientific way to measure it.

Number of Contact Pairs and Pinholes

The number of contact pairs can be selected according to the needs of the circuit, taking into account the size of the connector and the total separation force. The larger the number of contact pairs, the larger the volume and the larger the total separation force. In some cases where the reliability is high and the volume is allowed, the method of connecting two pairs of contact pairs in parallel can be used to improve the reliability of the connection. In the plug and socket of the connector, the pins (male contacts) and jacks (female contacts) can generally be assembled interchangeably. In actual use, it can be selected according to the live condition of both ends of the plug and socket. If the socket needs to be charged frequently, you can choose a socket with a jack, because the live contact of the socket with a jack is buried in the insulator, and it is not easy for the human body to touch the live contact, which is relatively safe.

Vibration, shock, collision

The electrical continuity of the contact pair when the connector is vibrated, impacted, and collided under the specified frequency and acceleration conditions is mainly considered. The contact pair will open instantaneously under this dynamic stress condition. The specified transient time is generally 1μs, 10μs, 100μs, 1ms and 10ms. The thing to pay attention to is how to judge the momentary failure of the contact pair. It is now generally believed that when the voltage drop across the closed contact pair (contacts) exceeds 50% of the power supply electromotive force, it can be determined that the closed contact pair (contacts) fails. That is to say, there are two conditions for judging whether an instantaneous interruption occurs: duration and voltage drop, both of which are indispensable.

Connection method

The connector is generally composed of a plug and a socket, in which the plug is also called a free end connector, and the socket is also called a fixed connector. The connection and disconnection of the circuit is realized by the insertion and separation of the plug and the socket, so various connection methods of the plug and the socket are produced. For circular connectors, there are mainly three ways: threaded connection, bayonet connection and self-locking (ball) connection. Among them, the threaded connection is the most common. It has the advantages of simple processing technology, low manufacturing cost and wide application range, but the connection speed is slow and it is not suitable for occasions requiring frequent plugging and quick connection. The bayonet type connection has a faster connection speed due to the longer lead of its three bayonet slots, but it is more complicated to manufacture and the cost is higher. The self-locking (ball) connection is the fastest connection among the three connection methods. It does not need to perform rotational movement, but only needs to perform linear movement to realize the functions of connection, separation and locking. Since it is a push-pull connection, it is only suitable for connectors with low total separation force. Generally more common in small connectors.

Installation method and shape

The installation of the connector includes front installation and rear installation, and the installation and fixing methods include rivets, screws, collars or quick locking of the connector itself. There is also a plug and socket that are both free-end connectors, the so-called relay connectors. The shape of the connector is ever-changing, and the user mainly chooses from the straight, curved, outer diameter of the wire or cable and the fixing requirements with the shell, volume, weight, whether it needs to be connected to a metal hose, etc. Connectors should also be selected from aspects such as appearance, shape, and color.

How to Choose a Low Frequency Connector (Part 2)

-Safety Parameters-

Insulation resistance

Insulation resistance refers to the resistance value that occurs when a voltage is applied to the insulating part of the connector, so that leakage current occurs in or on the surface of the insulating part. It is mainly affected by factors such as insulation material, temperature, humidity, contamination and so on. The insulation resistance value provided on the connector sample is generally the index value under standard atmospheric conditions. Under some environmental conditions, the insulation resistance value will decrease to an unnecessary extent. In addition, pay attention to the test voltage value of the insulation resistance. According to the insulation resistance (MΩ) = applied to the insulator voltage (V) / leakage current (μA) to apply different voltages, there are different results. In the test of the connector, the applied voltage generally has three grades: 10V, 100V, and 500V.

Pressure resistance

The withstand voltage is the critical voltage that can withstand higher than the rated voltage within a specified period of time between the mutually insulating parts of the contact pair or between the insulating part and the ground without causing breakdown. It is mainly affected by contact pair spacing and creepage distance and geometry, insulator material as well as ambient temperature and humidity, atmospheric pressure.


Any connector is inseparable from the current when working, which has the risk of fire. Therefore, the connector is required not only to prevent ignition, but also to self-extinguish within a short period of time once ignition and fire occur. When selecting, pay attention to choosing electrical connectors with flame-retardant, self-extinguishing insulating materials.

How to Choose a Low Frequency Connector (Part 1)

-Electrical Parameters-

Rated voltage

The rated voltage, also known as the working voltage, mainly depends on the insulating material used in the connector and the distance between the contact pairs. Certain components or devices may not perform their intended function below their rated voltage. The rated voltage of the connector should in fact be understood as the maximum working voltage recommended by the manufacturer. In principle, the connector can work well below the rated voltage. Therefore, we need to select the rated voltage reasonably according to the withstand voltage (electric strength) index of the connector, the use environment and the safety level requirements.

Rated current

The rated current is also called the working current. As with the rated voltage, the connector generally works well below the rated current. In the design process of the connector, the rated current requirement is met through the thermal design of the connector, because when the contact pair has current flowing, the contact pair will heat up due to the conductor resistance and contact resistance. When its heat exceeds a certain limit, it will destroy the insulation of the connector and form a contact to soften the surface plating, resulting in failure. Therefore, to limit the rated current, in fact, limit the temperature rise inside the connector not to exceed the specified value of the design. The problem to pay attention to when choosing is: For multi-core connectors, the rated current must be derated. This should be paid more attention in the occasion of high current. For example, the rated current of φ3.5mm contact pair is generally 50A, but the rated current of 5 cores should be derated by 33%, that is, the rated current of each core is only 38A. The more, the greater the derating.

Contact resistance

Contact resistance refers to the resistance generated by two contact conductors at the contact part. Two problems should be paid attention to when selecting: First, the contact resistance index of the connector is actually the contact resistance, which includes the contact resistance and the contact resistance to the conductor. Usually the conductor resistance is small, so the contact pair resistance is called the contact resistance in many technical specifications. Second, in the circuit connecting small signals, it is necessary to pay attention to the conditions under which the given contact resistance index is tested, because the contact surface will adhere to the oxide layer, oil or other pollutants, and the surface of the two contacts will produce film resistance . When the thickness of the film increases, the resistance increases rapidly, making the film a poor conductor. However, the membrane layer will undergo mechanical breakdown under high contact pressure, or electrical breakdown under high voltage and high current.

Shielding (anti-interference)

In modern electrical and electronic equipment, the ever-increasing density of components and the related functions between them imposes strict limits on electromagnetic interference. Therefore, the connector is often closed with a metal shell to prevent internal electromagnetic energy radiation or interference from external electromagnetic fields. At low frequencies, only magnetic materials can significantly shield the magnetic field. At this time, there are certain regulations for the electrical continuity of the metal casing, that is, the contact resistance of the casing.