A few months ago when I was interviewing a candidate for a new position at InterConnect I asked the prospect if he had any questions for me. He had a few about the company but he also asked two about aircraft. His first question was “How many wiring harnesses are there in an aircraft?” I said that it varies but generally-speaking, based on my almost 30 years of designing wiring harnesses, aircraft typically have around 250 wiring harnesses. I thought that was a good question. His second one was even better. He asked “Why do aircraft have wiring harnesses?” I told him that answer is a little more involved.
When aircraft were first designed, none of them had wiring harnesses because there were no electrical systems. All they had were structural components and ropes and pulleys to move the flight control surfaces. Soon, instead of ropes they used metal cables (and many aircraft still fly using metal cables and pulleys as opposed to ‘fly by wire’). One day an aircraft designer decided to put in an electrical light in an aircraft so he installed in a battery, a switch, and a light. He ran wires to these components and thus the first aircraft electrical lighting system was born. This system needed very few wires so each wire was installed one at a time in areas that protected the wires from external conditions.
Next, other designers came along and added more electrical systems. Each one of them required more wires. In time, aircraft mechanics started noticing that groups of wires ran from one component to another but they were installing wires one wire at a time. This installation process was time consuming. In order to speed-up the process, they started bundling groups of wires together and routing them together. Aircraft designers took note of this and thought that it was a good idea. They then designed the bundles of wires into a single unit and made them on a table. When they did this they designed the first wiring harness. That is why aircraft have wiring harnesses.
