"VW’s New Modular Wiring System
By Rod Young
August 1990

The press release kit for the new Passat is more like a book than a brochure; there is so much of it. One of the things that really stood out for me, because I have an interest in such things, is the advances made in the new Passat in the area of its electrical system.

The new B3 Volkswagen Passat features state-of-the-art electronics, and a clean-sheet approach to installing and maintaining electrical components.

After an in-depth, in-service study of where existing cars suffered electrical faults, and the time and methods used to track down these faults, Volkswagen’s engineers discovered that the most common place for an electrical fault was at connection points. The reason that faultfinding took so long was because vehicle technicians had to work through an entire wiring loom to discover where the fault was located.

To tackle both of these problems, Volkswagen engineers decided to abandon the traditional wiring loom, which resembles a domestic wiring system in which a whole range of sockets, or in the case of a car, components, share the same electrical loom, despite a wide variance in electrical consumption needs. Instead, Volkswagen has opted for a system owing more to a computer, in which individual components or small groups of components, have their own separate wiring system.

In practice this means that where the B2 (second generation) Passat had seven separate electrical looms, each supplying 20 to 26 different electrical components, the latest Passat possesses 26 different wiring looms, each controlling just six or eight components.

Because of this ‘modularisation’, a technician merely has to check a maximum of eight connections to track down a fault in a wiring loom, compared to 26 in the old car. To ensure that these connections are more reliable, Volkswagen has used an ‘error-free’ type of connector, as used in computer systems, that ensures accurate transmission of data, let alone the much more simple transmission of power.

All wiring looms are not only colour-coded in the traditional fashion, but also a coded message is printed on one side, indicating exactly what the loom controls. In the same manner, every electrical connection indicates to which loom it belongs, and what it is controlling.

All these wiring looms run into and out of a newly designed fuse box and relay plate, in which solid-state electronics have replaced traditional wiring and relays. Unlike traditional fuse boxes and relay plates, the new Passat system has been designed so that the whole box can be detached from the car and checked separately, thus speeding faultfinding and repair.

In designing this new type of electrical system, Volkswagen took into account the varying needs of Passat owners, and for this reason plenty of spare capacity has been built into the system so that accessories may be easily attached to the system. In all, there is space for 200 connections from the central fuse/relay box.

The decision was also made to retain the standard 12-Volt electrical system, and not use a micro-voltage switching system used by some manufacturers, so that all 12-volt accessories could be used in the new Passat without any modifications.

I’m fairly drooling to see this sort of equipment in the flesh. Volkswagen already has some of the most advanced electrical systems of any car manufacturer, but then made the Passat’s a whole lot better. I’ve seen a picture of the new fuse/relay box, and it looks incredible.

It’s at this level of design where Volkswagens, and probably all German cars, are different from other cars. When working with VW electrical systems, you can just about get inside the designer’s head, know what was going on and appreciate that these bits were designed to be worked on (by someone with knowledge and logic facilities, that is). On other cars, the only feeling you get is that the electrics were designed for cheapness and ease of assembly, and what happens after that is the owner’s problem.

The old VW wiring looms were superbly designed, but I’ve seen some crook things done to them by people who knew nothing and cared even less. On the new Passat, I hope it will be harder for these people to do their worst".

Electrical - Club VeeDub