Automotive wire harness routing involves determining how the wires in a vehicle will physically run from the power source to the components via modules.
Cars have complex wiring systems comprising multiple interconnected electrical parts.
Proper routing ensures the system remains safe, efficient, and reliable throughout the vehicle’s lifespan.
Let’s break down this cable management process to see what it entails. Read on to learn more!
Table of Contents
- Automotive Wire Harness Routing Aspects
- Wire Harness Design and Routing Best Practices
- Factors To Check in a Wire Harness
- Other Factors To Consider
- Wrap Up
Automotive Wire Harness Routing Aspects
Consider the following ten aspects when handling the car cable harness routing and packaging process.
Design and Layout
Before getting into the electrical harness installation, create a detailed design and layout of the electrical connection.
While laying out these wiring harness routing paths, identify all the electrical components, their location, the wires that connect them to the system, and the shortest path between them and the power source.
Pick the correct wire type and gauge after determining the shortest path between the components and their connection points.
For instance, you should use a double-core wire for the speakers.
Parts like tail lights need multiple cables because they have several bulbs in one.
Complex wiring harnesses with varying gauges bundled together
While at it, determine the most suitable wire gauge for the different parts. Tail lights usually require 16-gauge wires, but they can be thinner if the car features LEDs.
LED lights consume significantly lower power than regular bulbs, allowing you to use 18-gauge wire, which is cheaper.
When determining the wire gauge and type, consider the distance path, voltage levels, electrical current load, environmental conditions, and temperature resistance.
Even if you pick wire types with a tough outer layer that is moisture and temperature-resistant, you should include an outer layer to protect the wires from harsh environmental conditions.
Therefore, you should use corrugated tubes (convoluted tubing), braided sleeves, and rubber grommets to safeguard the different wiring harnesses.
Engine wiring harnesses covered with corrugated tubes
Also, you can combine separate wiring harnesses into a single wire loom to simplify the installation of the complex cabling while protecting them as one package.
A vehicle’s frame or chassis usually has channels for wire routing neatly within. These dedicated paths keep the wires organized while preventing damage due to extreme vibrations, friction, or tangling.
Channeling a sub-harness group or sub-harness without branch cables is easier than handling a complex configuration with multiple branches.
Cable Ties and Retaining Clips
The wire harness or loom channels in vehicles can sometimes be open paths that don’t lock the cables inside.
Even if the dedicated channel is inside the frame, you need a cable tie to hold the multiple wires as a single package.
A wire harness held in place using retaining clips
On open routing channels, you must use retaining clips on clip holes to aggregate the bundled multiple sub-harnesses to the vehicle to prevent excessive movement.
Otherwise, the wire insulations can experience friction and short circuits if the copper wires get exposed. You can use cable clamps in place of retaining clips.
Separate Power and Signal Cables
Car components are not the same. Some have a high power consumption while others draw little power.
Those with high power consumption, such as the ignition system components and starter motor, require thick, low-gauge wires. These cables usually emit electromagnetic or radio frequency waves that cause interference in nearby wires.
A car’s starter motor
Therefore, you should not place these wires near low-power signal transmission lines to maintain signal integrity. Otherwise, these lines will experience interference, affecting the signal going to or coming from the connected device.
Electromagnetic Interference Considerations
Signal or electricity supply cables might have to pass through areas with EMI or electrical noise. Such instances require you to route noise-resistant wires, such as those with braided or foil shields.
Twisted pair cables also help cancel EMI waves and perform even better if they have an outer shield.
A twisted-pair cable
Wires become less conductive when hot. Therefore, you should pick wires with thick insulations if the harness passes near a heat source.
For instance, the oxygen sensor mounts on the exhaust line and gets hot the more you drive. Its cable should have thick insulation to withstand the hot conditions.
An oxygen sensor (note the wire insulation)
Alternatively, these wires should have a secondary insulation, such as a heat-resistant convoluted tube.
Serviceability and Repair
These electricity supply and communication cables can experience damage or fail at some point when the car is in use. When determining the routing path, pick the one that is easily accessible to simplify the repair process.
Automotive wire harnesses undergoing repairs
Similarly, the correct routing path should place the components in easily accessible spots to make troubleshooting and repairs more manageable.
Compliance with Standards
The Wire harness routing and packaging should adhere to industry regulations and standards to maximize car and component safety.
Wire Harness Design and Routing Best Practices
Wire harness design and routing go hand-in-hand, so you should consider these best practices to get the cable harness to function optimally in its installed environment.
Get the Precise/Suitable Lengths of Wires
Check the precise measurements of the cables, including the bend radius, before cutting wires to attach to connectors.
Think of it as the running tracks in a stadium. In bundles, the bend radius of the inner cables will be shorter than those on the outer section.
Account for these length differences when routing the harness to have precise measurements before cutting.
Also, consider the length allowance for harnesses in flexible areas, such as car doors. They must be long enough to allow the door to open to the maximum point.
A car door wire harness with a section of it in a rubber grommet
Consider the Operating Environment
The harness channel might be through a hot, humid, cold, or radiated area. When routing wires through these parts, consider these “environmental” factors to ensure the harness can last and transmit signals with zero failure.
Factors like wire insulation and secondary protection play a significant role here.
Consider the Correct Routing
The car might have multiple routing options, but always pick the optimal channel with the lowest exposure to environmental conditions, length, and cost.
Automotive wire harnesses should fit neatly in their installation areas with zero hanging. So, use the required cable ties and clips with a short spacing to secure the wire firmly.
Joints and Protection
If you have to place mechanical joints, terminals, or cable protection in flexible areas, such as door openings, use one or more of the following items.
- Over-molded connectors
- Ultrasonic welds
- Solder joints
- Strain reliefs
Factors To Check in a Wire Harness
Some of the factors you must check that determine the cable’s physical properties include:
- Sheath or insulation material (PU, PVC, TPE, or PTFE)
- Wire length (cable should reach the component while considering the bend radius)
- Cable harness tolerance (must be able to stand the test of time)
- Wire gauge (the wires must meet the load current and voltage requirements)
- Wire ends to determine the terminal type and coating, connector design, and connection points.
A car wire harness undergoing quality inspection
Other Factors To Consider
Lastly, consider these harness routing factors.
- Installation area: Will the wire loom or harness be inside or outside the vehicle?
- Flexibility: How often will the cable undergo flexing? Car door wire harnesses must be flexible enough to withstand repeated opening and closing at the grommet area.
- Local environmental and safety regulations: Ensure the wire and component selection meet the local standards. The installation and inspection processes should also adhere to these regulations.
- Temperature fluctuations: Factor in any temperature fluctuations in the installation area.
The automotive wire harness routing process requires careful planning, and you can use CAD software to simplify the task while optimizing the layout.
We recommend using this design software because it can help you highlight potential issues before physically laying out the cables.
And remember to test the harness layout to validate its integrity before releasing the vehicle to real-world driving.
That’s it for now! Find time to go through these automotive wire harness design steps to learn more about that process.