Three Investigators and the Secret of the Wiring Harness


To do good detective work, you sometimes have to leave your desk. Three employees of Mercedes-Benz Cars colleagues discover the secret of the legendary wiring harness in Transsilvania.

The curse of the unicorn, the valley of illusions, the castle of perdition. In the famous book series “The three Investigators” mysterious cases like these are solved by the three master detectives Justus, Peter and Bob. In our case it is Edgar, Nils and Johannes who seek to unravel the secret of the wiring harness. It’s a tricky challenge. How is it possible to put together more than 1,000 cables with a total length of over three kilometers in such as way that they fit into a Mercedes-Benz E-Class as a cable set? With all the devices linked up with the right connector? To find out, our investigators have traveled to automotive supplier Leoni, in Transsilvania in northern Romania. There has been a new plant operating in the town of Bistrita since the end of 2015. This is where 2,000 employees produce wiring harnesses for the E-Class series. 1,050 sets per day, in two shifts.

“We negotiate terms and conditions with our suppliers, but we only had a theoretical knowledge at most of the technical challenges involved. We wanted to change that,” says Edgar Hert, team leader for wiring harness procurement at Mercedes-Benz Procurement & Supplier Quality (MP). So Hert traveled to Bistrita together with his colleague Nils Buettner and developer Johannes Mickeler. One day of intensive instruction at the training center, one day working in production.

Production of the electric wiring harness is a complex matter. A great deal of the work is done by hand, as hardly any cable sets are alike. The dominant concept here “Customer Specific Requirements”. It is the vehicle’s equipment specifications that decide the cable configuration. With the maximum equipment available for the E-Class series this means 2,108 contacts, 1,130 different lines and a total cable length of 3,277 meters weighing in at 48 kilograms. And that is just for the frame floor system, i.e. the interior wiring harness. Installed in the form of a large H, i.e. on the left and right along the sides of the vehicle, with a transverse section in the middle. Plus there are the harnesses in the roof, doors, seats, cockpit and engine compartment.


Enough practice, time to get working


Leoni production manager George Diaconu gives words of encouragement: “You don’t have to do everything perfectly, but you should know about everything.” Fingers were rubbed raw in the training center, while all the working stages were explained, but on day two things get serious. Brief instructions on who does what, then off they go. Head-first into the cold water of day-to-day production. Our three investigators give their all. Threading, wrapping and connecting. How reassuring that there is a final quality control station at the end. The experienced employees help out when things go wrong. With one or two quick flicks of a Hand.

“You’re still a little bit slow, but after another two weeks of training you’d be up to speed”, says production manager George Diaconu. Buyer Nils Buettner is exhausted after his stint in production, but pleased about the knowledge he has gained: “I am now able to understand the complex production process much better. And I now know what the critical points are.” His developer colleague Johannes Mickeler adds: “I have seen the effects my work as an engineer have on the production process quite clearly. It’s quite possible that I will take a different approach in some respects in future.” For Edgar Hert it is mission accomplished: “In future we will be able to communicate with the suppliers on a completely different level.” So by traveling to Romania, our three investigators have discovered the secret of the wiring harness. Only the landscape of Transsilvania remains shrouded in legends.

Mar 07, 2017
Rasmus Muttscheller