Waterproof Wiring Harness: It Is a Necessary Design For Automobile Wiring Harness


The automobile wiring harnesses comprise low-voltage cables and wires that connect different electrical devices of the vehicle. It is like the nervous system of your car, and you need to ensure its protection and stability to keep your vehicle going. While designing the harnesses, it is essential to consider the working environment of every area so manufacturers can offer the required protection to the saddles. One of the most critical aspects of designing wiring harnesses is water resistance.  Let’s find out more about waterproof wiring harnesses in this article.

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Things to Consider when Making a Waterproof Design:

Why and where do you need waterproof wiring harnesses?

The wading depth of the car

Every car or vehicle has a wading line which indicates the water level of the deepest area of water that a car can cross when driving at 10km/h. The vehicle’s wading depth means the height of this wading line from the ground level. Manufacturers design the electrical system and consider the wading depth to keep all the electrical components above the wading line. Further, if some features are present below the wading line, they should have an effective waterproof treatment.

Based on the vehicle’s electrical components and wiring harnesses and the wading depth, you can divide the layout of the vehicle wiring harnesses into the following areas:

  • Cab and passenger compartment
  • The 4-door line above the wading line
  • The 4-door line below the wading line
  • Rear door
  • Rear bumper above the wading line
  • Back insurance below the wading line
  • The ceiling
  • The frame beam part of the engine room
  • The frame beam of the engine room/the peripheral portion of the engine
  • The front bumper
  • The chassis and four wheels

Dry and Wet area and waterproof harness area:

Based on the above classification of the vehicle’s wiring harness parts, the parts below the wading line are all wet areas. These include the part of the rear bumper below the wading line, chassis, and four wheels, the 4-door line below the wading line, and the front bumper are all wet areas. Additionally, front and rear-guard areas, rear door areas, ceiling areas, and engine room areas are also wet areas. In these areas, you can find several wiring harnesses, including the front cabin wiring harness, powertrain wiring harness, rear bumper wiring harness, four-door wiring harness, and the battery positive and negative wiring harness.

Indoor harnesses, below the wading line, only a low-voltage horn plug-in needs water protection. It is essential to design electrical connectors for these wiring harnesses for waterproofing to seal the rubber gaps of the parts perforated in the room to prevent water flow in the cab. Also, it is equally essential to protect the check-in points of the harnesses with heat-shrink tubes.

Dry Zone: Except for the above-wet areas, the remaining dehumidification area is a dry Zone. The wiring harnesses include ceiling wiring harnesses, right floor/left floor wiring harnesses, and instrument wiring harnesses. The plug-in wiring harnesses do not need water protection. However, for areas in direct contact with the outdoors, you must use a sealed cable tie buckle.

The Waterproof Design of the Wire Harness

The different waterproof design of the automobile wiring harnesses include:

Harness winding method

Harness winding methods are of four types:

  • Semi encapsulation winding method/ rough winding method
  • Thick winding method
  • 2/3 packaging winding method
  • Double winding method

Among all these methods, most vehicles use a rough winding method or semi-encapsulated winding method in which you can tie the wires into a bundle. In this, the width of the insulating tape is ½ times, and in the rough winding, the width of the insulating tape is 1.5 times. Ensure you do not expose the adhesive surface of the insulating tape.

The powertrain wiring harness and the adhesive wiring harness have direct contact with the outside world, and thus you need to treat them primarily to make them waterproof. The same is the case with door wiring harnesses, as they can come in contact with water during rain or car washing. With the semi-encapsulated winding method, you can prevent water ingression into a harness and thus prevent short-circuiting.

You must cross-wound the branches for wiring harnesses that need special protection against water. First, semi-encapsulate the wiring harness area and apply the waterproof ring or through-hole rubber sleeve.

automotive wiring harness with positive battery terminal

Image: automotive wiring harness with positive battery terminal

Waterproof Wiring Harness: Selection of waterproof connectors

The whole vehicle connector plays two roles; firstly, they ensure signal transmission’s reliability and provide insulation for circuit protection. Ensure that the connectors in the engine compartment have proper waterproofing; for example, they should have waterproof rubber sealing plugs. Secondly, you can use the connector with a positioning clip to prevent the movement of the connector.

When the waterproof connectors work, they generate heat at the contact point, causing a rise in the temperature. In general, the working temperature of the connector is equal to the sum of the temperature rise in the contact and the ambient temperature. Thus, you should always consider a waterproof connector’s temperature resistance feature while selecting a waterproof connector.

automotive connectors

Image: automotive connectors

Waterproof Wiring Harness: Sealing

You can use seals to protect the wiring harnesses inline points, grounding points, and via protection. According to the Siphon phenomenon, the electrical module’s internal temperature rises on working. However, when it stops working, the temperature falls, causing a decrease in the internal pressure. As a result, the water can penetrate from the loosely sealing places following the pressure difference. Sometimes, there are gaps in the copper wire strands that infiltrate the electrical module leading to its malfunctioning. In such a situation, you must seal the wiring harness inline and grounding points with a glued heat shrink tube.

If the wiring harness passes through a body sheet metal hole, you can use a protective rubber cover for extra protection. Generally, you can find two types of vias. First, a simple sheet metal hole does not involve any movable parts. In this, you need to pay attention to the relative position of the harness after and before the via. Keep the outdoor portion of the harness lower than the indoor part. Secondly, there is a sheet for the moving parts. For such details, you must consider the design of the rubber parts and the crossing points so that there is no friction and interference during movement. Also, consider the relative positions of the holes of the rubber parts and sealing. Try making the outdoor hole lower than the metal hole in the sheet.

Waterproof Wiring Harness: Wire harness arrangement protection:

Mainly, in all electrical systems, water penetrates the electrical systems through its gravity. Thus, apart from using waterproof materials for protecting the electrical systems, you should opt for a waterproof function through a three-dimensional layout. You need to consider the vehicle’s electrical device layout from the early stage. Put all the electrical installation points higher than the grounding point. Also, keep the installation direction downward to resolve the water seepage problem caused by gravity.

These include door wiring and rear wiring harnesses because they face raindrops. When they fall, move outside through the wire harness. Further, keep the wiring harness arrangement near the whole vehicle’s drainage system.


When designing wiring harnesses, it is essential to consider their waterproof design. If the waterproof design fails for any reason, it will result in abnormal functioning of the electrical systems. As a result, it will affect the comfort and safety of the vehicle. Once the design is complete, you must always check the reliability of the design through a waterproof design. Cloom is a leading manufacturer of automobile wiring harnesses. So, please feel free to contact us if you need them or some guidance from professionals.