Waterproof Wiring Harness:  Why is it necessary to incorporate waterproofing in your car’s electrical systems?

About Waterproof Wiring Harness, Automobile wiring plays an important role, just like your body’s nervous system.

It is responsible for all the signals and electric energy transmission to different parts of the vehicle.

Likewise, it needs protection from external environmental aspects like heat, water, sunlight, and anything harmful. 

Among all these aspects, incorporating the moisture-resistant design is the most critical task.

In this article, we will look deeper into the problem and what you should consider to solve it. 

Why do we need waterproof wiring harnesses?

Let’s check out the reasons step by step. 

Wading Depth of a Vehicle

You might have observed that on each vehicle, there is a line indicating the deepest water level it can cross at 10km/h.

This line is called the wading line; its height from the ground level is the “wading depth” of the vehicle.

While designing an automobile, the engineers consider these factors to fix the electric components above this line so they do not expose them to water.

If they have to set any component below this line, they apply an extra waterproof material over them. 

On these bases, you can divide all the vehicle wiring harnesses into the following parts. 

  • Ceiling
  • Front Bumper
  • Chassis and all wheels
  • Rear Door
  • Rear Bumper (above the line)
  • Back insurance (below the line)
  • Cab and Passenger side (compartment)
  • The 4-door line above the wading line
  • The 4-door line below the wading line
  • Frame beam part of the engine compartment
  • The peripheral portion of the engine/ frame beam of the engine

Dry and Wet Area, and Wire harness fixation

Large wide cable in car module

Caption: Large wide cable in car module

As we have classified the car portions, you can see which parts are more exposed to water.

These parts, like the chassis, wheels, front bumper, rear bumper, and the 4-door line, require waterproof treatment before setting it up in the car.

Additionally, some other components like lower areas of rear doors, front and back guard areas, ceiling, and engine rooms also get exposed to rain, etc. simultaneously. 

Now these parts have a significant amount of wiring in them.

It includes a front cabin harness, powertrain wiring, rear bumper, 4-door, and battery’s +ive and -ive wire harnessing.

All these harnesses require water protection, so they use electrical connectors to seal the parts and block the water flow.

Moreover, engineers use heat-shrink tubing to cover the check-in points. 

Except for the abovementioned areas, all the other vehicle parts are usually classified as the dry zone.

The ceiling, right/left floor, and instrument wire harness are here. These areas need little to no water protection since they are not exposed to water.

But, if the engineers see that they connect to the outdoors in any manner, it is obligatory to use a sealed cable tie buckle with them.  

How to design a waterproof wire harness? 

You can use the following methods to design a waterproof wiring harness for the vehicle. 

Rodent Damage to the car wiring

Caption: Rodent Damage to the car wiring

Wire Harness Arrangement protection 

Playing with the harness position and arrangement allows you to achieve water resistance without using fancier components.

If it lays flat, water tends to seep into the wiring due to gravity.

To cater to the issue, you can use a three-dimensional design from the beginning of the vehicle manufacturer and fix the wires according to it. 

Moreover, the grounding point of the wires can be a weak link.

So fixing the wires above the ground level can also lessen the water penetration inside them.

However, you must still use effective insulation on each wire to minimize risks. 

Another vulnerable area of the vehicle in terms of moisture is the one close to the water drainage point, which includes door and rear guard wire harnessing.

The arrangement of the wires can also protect you from the water seepage in this area.

You only need to fix the harness at an angle that can flow the incoming water outside the car.

That way, there will be no intact droplets, and you will receive maximum protection. 


Using seals for protecting critical points of the vehicle is an old yet effective method.

You may have observed that the temperature rises as they move and falls off as the vehicle stops working.

The siphon phenomenon indicates the same behavior, pointing out that the occurrence of pressure differences causes water to seep in. 

Water can attack the gaps in copper wires while damaging the electric system.

Hence to fill in these gaps, you can use glued heat-shrink tubing.

Furthermore, if the harness involves a metal sheet, you can use rubber covers for insulation.

Here you can find two types of metal shield installation, one with a fixed wire harness and the other for moveable parts. 

To fix the wire harness, you have to look for the position of the harness before and after the installation.

Also, you will keep the indoor harness slightly higher than the outdoor one. 

If the sheet connects moveable parts, your best bet is to use rubber insulation so that there is little to no friction in the movement of the components.

Moreover, consider the position of the holes of these parts and make the outer hole lower than the metal sheet’s hole. 

Selection of Waterproof Connectors

A vehicle’s connections can be used for linking two wires together and providing protection to the joining points.

Hence, making connectors with proper waterproof sealing plugs and clips in place would be best. 

Another point to consider before choosing a connector is that these joining points dissipate heat while working.

As per the rule, the amount of heat a connector can endure is the sum of temperature rise and the ambient temperature of the contact.

Hence, buy connectors compatible with your vehicle’s heat dissipation.

You will also face connector melting, which will destroy the electric module. 

Waterproof connectors in the car wiring system

Caption: Waterproof connectors in the car wiring system

Harness Winding Method

For extra protection, you can use four harness winding methods. It includes 

  • The whole vehicle winding
  • Thick winding 
  • Double winding 
  •  ⅔ winding package methods. 

You can adopt two methods: semi-encapsulation and in-vehicle winding, rough winding.

In semi-encapsulation, you will bind the wires into a bundle using insulation tape at intervals half the tape’s size.

On the other hand, in the rough wind, you will bind the wire bundle with tape spacing 1.5 times the tape width.

Ensure that the tape’s sticking side is not exposed to the air. 

You must apply special waterproofing treatments for critical wire harnesses like powertrain and adhesive ones, as they are usually exposed to the environment.

Moreover, the door wire harness also requires extra protection as water splashes onto them while car washing and rain.

The semi-encapsulation works best to stop water penetration and prevent short circuits. 

Additionally, you can use the cross-wounding on any exposed wires.

First, you can semi-encapsulate the wire harness and apply the waterproof rings and through-hole rubber sleeves. 


Water protection is a must while dealing with electrical components since continuous exposure to moisture encourages oxidation, and the wires’ performance also deteriorates with time.

In addition, non-functioning wires may result in complete failure most of the time.

Cloom has had expertise in automotive wire harnesses for years and can design one for you with all the considerations on hand. 

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