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Knowledge Points Of Automobile Wiring Harness Fastening Bolts

Sep 01, 2020

Most automobile wiring harnesses use M5, M6, M8 bolts or nuts to tighten the connection hole-type terminals or fuse components. This article focuses on the bolt connection of the fuse box in the automotive wiring harness, the fuse in the central electrical box, the power cord terminal, and the dynamics in the bolt connection Torque, static torque, and torque attenuation are several aspects.

In the production process of automobile wiring harness, some wire-hole terminals, fuses, connecting pieces, etc. need to be tightened with bolts. The clamping of the positive and negative terminals of the power wiring harness also needs to be clamped with bolts.

Most automobile wiring harnesses use M5, M6, M8 bolts or nuts to tighten the hole-type terminals or insurance components. The bolted components are mainly in the central electrical box, the fuse box of the front wiring harness, the fuse box of the instrument wiring harness, and the fuse of the power wiring harness. Box and the positive and negative connectors of the power harness.

However, the functional and performance requirements of these bolted components are relatively high, and the failure of the bolt or nut tightening connection will directly affect the safety of the automobile wiring harness, and even cause serious car burning accidents.

Therefore, the use of a reasonably designed bolt tightening connection plan, the correct use of bolt tightening tools, and an effective bolt tightening inspection method are important factors to ensure that each bolt in the wiring harness is tightened correctly.

Concepts related to tightening of automotive wiring harness bolts

Common connection methods in automotive wiring harnesses include:

Ultrasonic welding, resistance welding, cold stamping connection, bolt tightening connection, riveting, bonding, etc., among which bolt tightening connection is simple and convenient, can be disassembled and reassembled many times, standardized components, and saves costs.

Bolt tightening connection is usually divided into two types: hard connection and soft connection.

Soft connection refers to the connection that reaches the target torque after 2 turns (720°) after reaching the bonding point. Common flexible connections include the connection between plastic and metal or between plastic and plastic, and the connection between fuse box and fuse. The bolts tightened and clamped in the automobile wiring harness are mostly copper and zinc materials, which are soft connections.

Hard connection refers to the connection that reaches the target torque within 30° after reaching the bonding point; common hard connections include connections between engine cylinder blocks, automobile chassis bridges, and steel components.

Fitting point: The connection state where the clamped objects stick to each other after the bolt tightening connection reaches the target torque clamping.

Control methods and advantages and disadvantages of bolt tightening connection

The control methods of bolt tightening connection include: 1. Torque control/angle monitoring, 2. Angle control/torque monitoring, 3. Torque and angle control.

Torque control: refers to the setting of the maximum torque value of the tightening tool, and the tightening ends when the value is reached; the torque control method is to provide the minimum clamping force when the maximum friction coefficient and the minimum torque appear.


1. It is easy to realize the control of different accuracy levels, from ±25% pulse-type tools to ±-1% manual tightening of shafts (sleeves).

2. Has a large number of standard data for product and process design, and has a long application history.

3. It is very easy to verify the validity of the process and equipment.

4. Engineers are very familiar and well-known;


1. The accuracy of the clamping force is very poor, possibly up to ±60%, which is greatly affected by the friction coefficient.

2. There is no fundamental way to prevent the bolt from breaking.

3. The above two reasons lead to a low utilization rate of bolt capacity by ±60%.