Design points of wiring harness in vehicle layout

Blog | news | Feb 11,2023

As an important part of connecting electrical devices in a car, the wiring harness, its design and implementation, and the reliability of the vehicle layout play an important role in the realization of electrical functions. It is called the nervous system of the car.

With the increase in electrical functions of the vehicle and the widespread application of electronic control modules, there are more and more electrical components and more and more wires, and the wiring harness becomes thicker and heavier. How to make the wiring harness more compact in the limited car space? It has become a problem that must be solved to effectively and rationally arrange the wiring harness of the car to play a greater role.

Design principles of wiring harness in the vehicle wiring

The wiring harness itself is soft and easy to bend, and it has strong adhesion in the layout. It is generally arranged along the front and rear longitudinal beams, round beams, and parts fixing brackets of the car body. The usual fixing methods are fixed by wire clips and buckles. wait.

No matter what kind of fixing method is adopted, the wire harness will touch different parts in the direction. Some parts will not be affected by the contact with the wire harness.

Abrasion or extrusion interference requires consideration of various factors, mainly the following principles:

  • Avoid contacting the wire harness with the surface of sharp and easily worn parts;
  • The two fixed points of the wire harness should not be too tight, and the direction should be smooth without distortion;
  • The wiring harness needs to be kept away from heat sources or has corresponding protective measures;
  • The branch wire harness must be reserved when it comes out of the main line to prevent it from being squeezed, entangled or going in the wrong direction;
  • There must be a space between the wiring harness and the moving parts.
  • According to the above principles, summarize the layout requirements of the wiring harness on the vehicle.

When making the layout of the wiring harness of the vehicle model, confirm the distance between the wiring harness and the surrounding parts according to the requirements. If the requirements are not met, it is necessary to change the direction or increase protection and other measures to optimize the design.

Orientation design method of key positions

A set of vehicle wiring harness runs through every electrical appliance in the front cabin, cockpit, chassis, door, etc., so the length of the wiring harness is relatively long and the distribution is scattered.

Therefore, it is necessary to review each position of the wiring harness to evaluate whether it meets the requirements. The requirements for the surrounding space of the wiring harness and key positions need to develop design methods to avoid risks, which are introduced one by one below.

Waterproof requirements

The connection between the front cabin wiring harness and the cockpit wiring harness.

When the front compartment wiring harness is connected to the cockpit wiring harness, it needs to pass through the dash panel of the vehicle body. Because the cockpit is an indoor space with good sealing performance, water leakage, and dust leakage are not allowed, so the wiring harness design at this position needs to consider the waterproof requirements.

The following design requirements are required for sealing and waterproofing:

Waterproof between the sheath and the sheet metal: the design fit size between the through-hole sheath and the dash panel needs to be oversized, and It can be completely sealed after being assembled in place;

Waterproof between the sheath and the wire harness: the inner diameter of the sheath through the wire harness must be smaller than the outer diameter of the wire harness to prevent water from entering from the inner diameter of the sheath;

Water enters the wiring harness corrugated pipe: the reason for the layout space of the wiring harness outside the cockpit is that Z is higher than the through-hole sheath upwards, and the water flows into the cockpit along the corrugated pipe. Therefore, it is necessary to conduct water at the lowest point outside the cabin to prevent water from entering the inner cabin. The measure is to disconnect the bellows and replace them with cloth tape;

Water guide in the wiring harness: because the wiring harness is covered by an open bellow, water can easily enter the gap between the wires after entering the bellows. When the rainfall is too heavy, water can easily enter along the wires. Therefore, it is necessary to add waterproof cement between the wire and the wire at the position of the via-hole sheath to seal.

The above four points should be considered when designing the wiring harness, and corresponding measures should be formulated to seal them to prevent water from entering the room and causing parts such as carpets to get wet.

Anti-extrusion requirements

Wiring harness through the door sill floor position

The laying of the wire harness along the sheet metal through the inner panel of the door sill is an invisible part, so the following aspects need to be considered in this position:

The door sill trim panel extrudes the wire harness as a necessary place for getting on and off the car. The door sill’s inner panel will often be stepped on, and the resulting deformation will act on the wire harness passing through this position.

If the trim panel deformation is too large, it will cause the wire harness to be deformed and worn after being stressed. Therefore, the wiring harness at this position should be routed in a flat panel to avoid squeezing the wiring harness when the interior pedal is stepped on.

The outlet position of the small branch of the harness is close to the fixed point. After the small branch appears, it is fixed on the sheet metal, which is close to the fixed point. If the trunk line of the harness is subjected to a downward force,

It is easy to cause the branch to be pulled, or contact and wear with the raised part of the ground sheet metal, causing line failure and functional failure. Therefore, the outlet position of this small branch needs to be changed to avoid the risk of the pedal being squeezed.

As mentioned above, if the wiring harness is arranged near the moving parts, it is necessary to simulate the movement mode and amplitude of the moving parts, and if there is interference and extrusion, it is necessary to optimize the direction in time to avoid risks.

Process assembly requirements

The layout of the wiring harness at the place where the bolts are fixed

The wiring harness belongs to the electrical device connection material of the whole vehicle, and it belongs to the relatively front position in the assembly process. After the wiring harness is arranged, when other parts are fixed, if the assembly equipment interferes with the wiring harness, there will be a risk that the wiring harness will be squeezed and damaged, resulting in functional failure.

The wire harness runs under the fixing hole of the seat belt. Because the wire harness is softly routed, there are two routing methods. The wire harness in the second picture is relatively close to the fixing hole, and there is a risk of pinching the wire harness when assembling the seat belt.

Therefore, this position needs to move the buckle position of the wire harness and place it under the fixing hole. This measure can avoid squeezing the wire harness, avoid interference from the design, and reduce the risk of process control. If you need any help finding the right product for your application, please contact us at and we will be happy to assist you.

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