What is a wire harness?

The Wiring Harness is a wiring component that connects various electrical equipment in a circuit, and is composed of an insulating sheath, a wiring terminal, a wire, and an insulating wrapping material.
1. The composition of the Wire Harness
1) Wire harness
In order to facilitate installation and maintenance and ensure that the electrical equipment can work under the worst conditions, the wires of different specifications and colors used in the electrical equipment of the whole vehicle are rationally arranged and integrated, and the wires are bundled with insulating materials. In bunches, it is both complete and reliable.
2. Normal selection of wire cross-sectional area and color code
1) Correct selection of wire cross-sectional area
The electrical equipment on the vehicle selects the cross-sectional area of the wires used according to the load current. Electrical equipment that works for a long time can choose 60% of the actual current carrying capacity of the wire; electrical equipment that works for a short time can use 60%-100% of the actual current carrying capacity of the wire.
2) Selection of wire color code
For easy identification and maintenance, the wires in the harness are colored differently.
For the convenience of marking in the circuit diagram, the colors of the wires are represented by letters, and the colors represented by them are noted in each circuit diagram.
3.The main reasons for the failure of the wiring harness
Common faults in automobile lines are: poor contact of connectors, short circuit between wires, open circuit, grounding, etc.
The reasons are as follows:
1) Natural damage
The use of the wire bundle exceeds the service period, which will cause the wire to age, the insulation layer will be broken, and the mechanical strength will be significantly reduced, causing short circuit, open circuit, grounding, etc. between the wires, causing the wire bundle to burn out. The wiring harness terminals are oxidized and deformed, resulting in poor contact, etc., which will cause the electrical equipment to not work properly.
2) Damage to the wiring harness due to failure of electrical equipment
When the electrical equipment is overloaded, short-circuited, grounded and other faults, it may cause damage to the wiring harness.
3) Human failure
When assembling or repairing auto parts, the metal object crushes the wire harness and breaks the insulation layer of the wire harness; the position of the wire harness is improper; the lead position of the electrical equipment is connected incorrectly; the positive and negative leads of the battery are connected reversely; Connecting, cutting the wires of the wire bundles randomly, etc., can cause the abnormal operation of the electrical equipment, and even burn the wire bundles.
4. Detection and judgment of wiring harness line faults
1) Detection and judgment of wire harness burnout fault
The burnout of the wire bundle occurs suddenly, and the burning speed is very fast. Generally, there is no safety device in the burned out line. The rule of wire bundle burnout is: in the circuit of the power supply system, wherever the wire is grounded, the wire bundle will be burned, and the junction between the burnt and the intact part can be considered to be grounded; if the wire bundle is burned out When it reaches the wiring part of an electrical equipment, it indicates that the electrical equipment is faulty.
2) Detection and judgment of short circuit, open circuit and poor contact between lines
The wire bundle is squeezed and impacted by the outside, causing damage to the wire insulation layer in the wire bundle, resulting in a short circuit between the wires, causing some electrical equipment to be out of control and fuses to blow.
When judging, the wire harness connectors at both ends of the electrical equipment and the control switch can be disassembled, and the short circuit of the line can be detected with an electric meter or a test lamp.
In addition to the obvious fracture phenomenon, the common faults often occur between the wire and the wire terminal. After some wires are disconnected, the outer insulation layer and wire terminals are intact, but the inner core wire and wire terminals of the wires are disconnected. When judging, a tensile test can be performed on the conductive wire and wire terminal suspected of being broken. During the tensile test, if the insulation layer of the wire gradually becomes thinner, it can be confirmed that the wire is broken.
The line is in poor contact, and the fault mostly occurs in the Connector. When a fault occurs, it will cause the electrical equipment to not work properly. When judging, turn on the power supply of the electrical equipment, touch or pull the relevant connectors of the electrical equipment, when touching a certain connector, the electrical equipment works normally or not, indicating that the connector failure.
5. Replacement of wire harness assembly
1. Appearance inspection
1) The model of the new wire harness should be the same as the original model, the wire terminals and wires are connected reliably, and each connector and wire can be pulled by hand to see if there is any looseness or falling off.
2) Compare the new wire bundle with the original wire bundle, such as: the size of the wire bundle, wire terminal joints, wire color, etc. should be basically the same. If there is any doubt, test with a multimeter and confirm that the wire harness is in good condition before replacing it.
2. Installation of wiring harness
The connectors, plugs and sockets of each electrical equipment must correspond to the sockets and plugs on the wire harness. After each connecting wire is connected to the electrical equipment, there must be a certain margin, and the wire should not be pulled too tightly or placed too loosely.
3. Line inspection and connection test
1) Check the line
After the wiring harness is replaced, firstly check whether the connection between the wiring harness connector and the electrical equipment is correct, and whether the positive and negative electrodes of the battery are connected correctly.
2) Power-on test
The ground wire of the battery can be temporarily disconnected, use a 12V, 20W bulb as a test light, connect the test light in series between the negative electrode of the battery and the ground end of the frame, and turn off all electrical equipment switches on the car. The test light should not be on when it is normal, otherwise it indicates that the circuit is faulty. When the circuit is normal, remove the bulb, connect a 30A fuse in series between the negative electrode of the battery and the ground terminal of the frame, do not start the engine, and turn on the power of each electrical equipment on the vehicle one by one. And circuit inspection, after confirming that the electrical equipment and circuit are correct, remove the fuse, and connect the battery ground wire.