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How to choose a waterproof plug for a car wiring harness connector?

How to choose a waterproof plug for a car wiring harness connector?

Blog | Jul 18,2023

In the car, the whole vehicle can be divided into dry area and wet area. There are differences between dry and wet areas. As the neurons of the car, the waterproof performance of the wiring harness in different areas also has different protection level requirements, which can ensure the normal operation of the entire circuit. Wiring harnesses with different levels of protection can ensure that the performance of the vehicle is in the best state during operation.

After the selection of the waterproof plug after the connector is selected, there are also several important parameters to refer to, such as: the inner and outer diameter of the waterproof plug, the outer diameter of the blind plug, the inner diameter of the connector hole, and the outer diameter of the wire insulation. Whether the relationship between these data matches well determines the stability of the waterproof performance of the waterproof connector in the car under various working conditions.

How to select the sealing plugs?

The following is some introduction to the selection of sealing plugs.

1.Definition of the wet area in the middle area of automotive wiring harness

Dry area: The wiring harness installed in the cab, crew room, luggage compartment, etc., does not need to do special waterproof protection treatment area.

Wet area: The area where the wiring harness requires special waterproofing, except the dry area.


2.Definition of sealed wire and connector lumen in wiring harness

It is used to isolate the connecting part of the connector and the outer wall of the wire from the external environment. Sealed wire is also called waterproof peg or waterproof plug, which plays a role of protection and sealing. It is usually a soft rubber piece, which is used to plug the socket of the connector without the wire inserted, and the sealing function is the blind plug; generally, there are two states: soft rubber and hard plastic rod. In special cases, the connector itself has a waterproof rubber pad.

The principle of waterproof plug selection

Under normal circumstances, when the waterproof connector is in the factory, the waterproof level of the plug has been determined, and the required sealing plug is also developed accordingly. If the wiring harness factory faces a relatively single customer and the product type is relatively single, then the selection, procurement, storage and use process of the waterproof plugging material is also relatively simple and convenient. However, as the wiring harness factory faces more diversified customers and the product types are more complicated, the selection, procurement, storage, and use of waterproof plugging materials are very complicated tasks for the procurement and management departments of the wiring harness enterprise. In order to simplify the process, corresponding integration can be carried out according to the following rules, reducing the types of materials and reducing the pressure on procurement and storage.

The waterproof performance is reflected by relying on soft rubber parts to fill the wire insulation layer with the inner hole of the connector, so as to isolate the inner cavity of the connector from the outside world. Plug the hole where the connector does not enter the wire with a blind plug to prevent liquid from entering. The size of the drain bolt, wire and connector should be closely matched.Connector hole inner diameter D1, wire insulation outer diameter D2, sealing plug inner diameter D3, sealing plug/blind plug outer diameter D4, as shown in Figure 1 below.

The relationship between the four kinds of outer diameters is as follows:

D1<D4, D3<D2

Considering the tolerances in the processing of connectors and sealing plugs, the relationship between the dimensions of the four outer diameters is:
D4-D1≥0.3mm, D2-D3≥0.3mm

Special attention should be paid to these dimensional relationships when selecting waterproof plugs.

Specifications for the assembly of waterproof bolts and blind bolts

The actual assembly of waterproof plugs and blind plugs is closely related to the waterproof performance of the connectors, and is a key factor to ensure the waterproof performance of waterproof connectors. Unless otherwise specified, waterproof plugs and blind plugs are not allowed to leak above the hole plane of the connector. Special connectors are implemented according to special requirements. In order to reduce the friction between the waterproof plug, blind plug and the outer wall of the connector, some silicone oil can be properly applied to increase the lubricity during implantation, but it is strictly forbidden to use machine oil instead.

When the waterproof plug is threaded on the wire, the leakage size of the wire insulation is also a critical size. Under normal circumstances, the wire insulation should leak outside the end face of the waterproof plug, but not more than 1 mm, as shown in Figure 3 below.

When the wire is sealed or crimped through the sleeve, avoid the sealing plug being pierced. After the waterproof plug is riveted through the sleeve,the wire conductor and the wire insulation layer should be visible in the connection area B. See Figure 4 below.

Waterproof performance verification

For the waterproof performance of waterproof connectors, different Oems have different requirements for the distribution of connectors. For example: some vehicle manufacturers require that the waterproof capacity of the connector in the wet area is required to reach IPX7, that is, it is required to prevent the effect of short time immersion, and the amount of water into the shell will not reach harmful levels after entering the water that reaches the pressure.The tested connectors are immersed in water according to the installation state specified by the manufacturer:

  1. When the height of the connector is less than 850 mm, the lowest point of the connector should be 1000 mm below the water surface.
  1. When the height of the connector is equal to or greater than 850 mm, the highest point of the connector should be 150 mm below the water surface.
  1. The duration of the test in water is at least 30 minutes.
  1. Thetemperature difference between the water temperature and the connector is not greater than 5K.
  1. If the waterproof test is carried out on the connector equipped with wires, the length of the wires must be greater than 1 meter to prevent the end of the wire from being immersed in water and the wire sheath from being damaged. There are gaps between the multi-strand copper wires of the wire core, and the insulation skin forms a pipeline. If the end of the wire is immersed in water, water can enter the cavity of the connector along the pipeline formed by the wire insulation layer.

After meeting the above conditions, if no water accumulation occurs, the waterproof performance is judged to be qualified. The verification method of waterproof performance test is shown in Figure 5.

The non-original connectors are matched with waterproof plugs and blind plugs.After selection and matching, it is necessary to pass the waterproof test before it can replace the waterproof plug and blind plug matched by the original connector.Substitutes that have not been verified by waterproofing tests shall not be used in actual manufacturing processes.


Combined with the actual processing practice and the above discussion, the following conclusions are drawn. The selection and application of the waterproof plug of the waterproof connector in the wiring harness directly affect the process quality of the product processing. Waterproof bolts/blind bolts, wires, and connectors must be closely matched. In the selection process of waterproof plugs and blind plugs, the corresponding integration can be carried out without violating the relevant quality requirements of matching gap size and crimping, reducing the types of waterproof plugs and blind plugs, and reducing the inventory and storage management of such products pressure.

In addition, this practice can bring the following benefits, such as, avoid the delivery pressure caused by the long procurement cycle of the original waterproof plug and blind plug and the tight delivery time of customers. It can also reduce the pressure caused by unstable order quantity, multiple varieties, multiple batches, and small single order capacity. It can save the cost of human resources, operation management and quality management within the company.

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