What’s a smart wiring harness?

A smart wiring harness implements protective functions like short circuit and over-temperature protection and reporting. By implementing common functions, they reduce the amount of wiring in the vehicle and eliminate the need for modules like fuse boxes. Smart wiring harnesses are found in military, construction, commercial, and public transport vehicles. They are beginning to find their way into light-duty internal combustion engines (ICE) and electric vehicles (EVs).

Improvements in wiring harness performance have been evolutionary, not a step function change. They began with the control area network (CAN), local interconnected network (LIN), and FlexRay technologies. CAN and LIN reduced the amount of wiring needed, simplifying the design of wiring harnesses (Figure 1). However, they are relatively slow and unsuitable for safety-related communications like wire-based braking.

Figure 1. Using a CAN bus can significantly reduce the complexity of wiring harnesses. (Image: NI)

FlexRay takes that evolution to the next level. It is about 10 times faster than CAN or LIN. More data can be carried on fewer wires, reducing wiring harness complexity, weight, and costs. The next step is adding intelligence to the harness with smart distribution modules.

Smart distribution modules

Smart distribution modules (SDMs) are common in emerging smart wiring harnesses. SDMs can include a microcontroller unit (MCU) to provide adaptability, edge processing of sensor inputs, and communication. SDMs are being developed for low-voltage and high-voltage wiring and specific lighting functions.

One SDM implementation supports six channels with up to 13 A of power per channel. It replaces switches, relays, actuators, fuses, and circuit breakers. The SDM provides enhanced performance, such as resettable and programmable electronic fuses. The system architecture includes a central bus bar for power transfer and a single communication wire for each SDM (Figure 2).

Figure 2. Block diagram of a smart wiring harness showing the positions of the multiple output SDMs (black boxes). (Image: Martin Technologies)

In addition to electronic fuses, an SDM can include sensors for overcurrent, overvoltage, or overtemperature on all powered devices. Detection can take place in less than a microsecond.

In some instances, communication can be sent over the power busbar, further reducing the wiring and harness weight. The basic system is designed to handle voltages from 5 to 60 Vdc. A high-voltage adapter board can be added to control EVs’ battery pack and drivetrain power. A fire prevention algorithm has been developed to analyze sensor data and identify possible fire hazards.

Retrofit harnesses for lighting

Specialized smart wiring harnesses have been developed to add or retrofit LED lighting into a vehicle. One key is a built-in microprocessor that automatically detects whether the existing system is positive or negative switched and adjusts the operation of the smart wiring harness accordingly (Figure 3).

Figure 3. Smart harness for retrofitting vehicle lighting systems. (Image: Stedi)

The retrofit kit also includes HB3 and H4 adapters. The HB3 adapter enables auxiliary lighting installation without splicing or soldering to the existing factory wiring. It’s often used to replace halogen bulbs with LEDs. The H4 adapter connects the headlights.