Blog

Quick peek on complex wiring harnesses

  • 28. November 2018

Just in time for IESF 2018 in Munich we received a little story on wiring harnesses.  Thanks for sharing this Vlad.

Some time ago I was pulled over by the Police because my rear fog light was not switched on although it was a misty morning. Only then did  I realize my dashboard warning light for the rear fog light had been on for quite some time. The Police was kind enough to give me a warning only, so I went to an auto repair shop to check that rear fog light.

Some time ago I was pulled over by the Police because my rear fog light was not switched on although it was a misty morning. Only then did  I realize my dashboard warning light for the rear fog light had been on for quite some time. The Police was kind enough to give me a warning only, so I went to an auto repair shop to check that rear fog light.

They checked it and told me right away the light bulb was not the problem.  They would have to change the entire rear bumper wiring harness that embeds the rear fog light, parking sensors, trunk courtesy light and also the left rear lamp. Plus the parking sensors! That intrigued me a bit since the cost was quite steep so I decided to fix this by myself.

On a sunny Saturday I pulled away the upholstery in the trunk of the car to reveal the faulty wiring harness. I finally found it, and right there on the spot,  I realized why wired networks are considered the backbone of complex systems.

There was an octopus-like wiring harness going in all directions, with all types of insulations, fixtures, connectors and so on. Considering that in the last few years industry has faced an exponential growth of electronic devices, this increase in the complexity of modern systems has come with the increase of wire lengths. This is not only true for all in-vehicle or in-airplane systems, but infrastructures and buildings as well.

The cumulated length of electrical wires in a modern car exceeds 4 km! This means there could be more than 1,000 meters of wiring I would have to check right there in the trunk.

Swiftly jiggling the harness branch I thought to be faulty, I noticed a wire was dangling.  Both ends were kept together by some insulation only. That was a quick fix for me and I was happy I was able to find the solution.

Nevertheless, there are a few ideas I would like to share here:

  • Go to an authorized dealership where they have all the electric diagrams of the car (plus the trained personnel) and may hopefully ?!?! debug this kind of situation.
  • The question that arises is where this increase in complexity will lead to and how large will the wiring harness grow? Whatever their application domain, wires can be subject to aggressive environmental conditions which may create defects; so these defects can have dramatic consequences – especially since in most cases the wires are in parts of safety critical systems.
  • So even for companies that produce low volumes & low complexity harnesses, the 1$ solution for harness design (that is the pen and paper) no longer succeeds. Schematic design and harness engineering may only be performed in a smart electrical CAD that enforces revisions, tracing, analysis, electrics -> wiring harness synchronization, mechanical CAD integration and smart documentation generation.