Understanding European DIN wiring

Understanding European DIN wiring

Seyfert, Karl

European wiring diagrams may look strange and incomprehensible. But they’re not so tough to understand when the underlying standards are explained.

Over the years, I’ve heard many explanations for why some technicians choose not to work on European vehicles. For some, it’s based on their desire to work only on vehicles built within our borders. For others, the choice may be based on the belief that European cars are just too “foreign” and their systems too unusual or exotic to easily understand.

In today’s automotive economy, it has become increasingly difficult to hold onto these attitudes. Many cars sold in this country by European (and Asian) manufacturers are actually assembled right here in the U.S. This blurs the conventional definition of an imported vehicle. At the same time, many “American” cars are actually assembled outside our borders, further confusing the accepted definition of a domestic car.

Auto manufacturing is truly a global enterprise, with all of the major manufacturers conducting business in several countries simultaneously. Even if we ignore the differences of language and culture, isn’t it still a difficult problem for a European manufacturer to build vehicles in a different country like the U.S.? To oversimplify the challenges involved, how do you get an American assembly line to crank out parts for a European car? The answer is standards. Standards have been an integral part of the automotive world since the earliest days of the automotive assembly line. Standardization of parts allowed automakers to transform their businesses from a one-at-a-time proposition to a many-at-a-time operation.

In this country, the Society of Automotive Engineers (SAE) is responsible for maintaining order by establishing many of the standards that apply to automobile manufacturing. When you pick a bolt for a domestic vehicle out of the bolt bin, chances are the standards and specifications concerning its thread pitch and hardness were originally defined by SAE. Thanks to standardization, that bolt should thread into any nut made anywhere in the world, as long as it conforms to the same set of standards.

In Europe, the most widely recognized organization responsible for establishing and publishing automotive standards is called Deutsches Institut fur Normung e.V Standards established by this organization are often referred to as DIN standards.

DIN standards have been established for a multitude of things, including many outside the automotive world, but we’ll limit the focus of this article to the DIN standards for automotive wiring. Why wiring? Because that’s the one thing I’ve heard the most techs complain about when it comes to working on European vehicles. For some, it’s the layout of the electrical components throughout the vehicle. For others, it’s understanding the wiring diagrams that map out the position and operation of all those systems and components. The diagrams may look strange and incomprehensible. But when you understand the underlying system and standards that were used to design the vehicles and the diagrams, it’s not as tough as it first seems.

Terminal Designations

DIN standard 72 552 establishes the terminal numbering system that’s used for any wiring diagram or vehicle wiring that conforms to DIN specifications. The terminal codes are not wire designations, as devices with differing terminal codes can be connected to the opposite ends of a single wire. The chart on pages 42 and 43 outlines many of the common terminal designations described under DIN 72 552. Some of the more obscure numbers, which refer to components on trailers, heavy-duty trucks and such, have been intentionally omitted.

When you’ve worked with DIN wiring for a while, you’ll begin to recognize certain numbers that come into play more often than others. For example, a terminal 31 designation always refers to a direct connection to vehicle ground and a terminal 30 designation always represents a direct connection to the battery positive terminal. And terminal 50 is always battery positive with the key ON or in the CRANK position.

Wire Color Codes

Before we get into some actual DIN wiring diagrams, a word about wire color codes. Most wiring diagrams you’re likely to come across will have already been translated into English. Wire colors in those diagrams should be labeled with abbreviations you’ll be able to understand. But just in case you run across a diagram with the original wiring color codes, use the “Wire Colors” key at left to sort things out. By the way, color codes for electrical wiring are defined in DIN 47 002.

Circuit, Block & Schematic Diagrams

Description of an electrical system or circuit may begin with a circuit diagram. This is an idealized representation, rendered in the form of symbols to provide a quick overview of circuit and device functions. The circuit diagram illustrates the functional interrelationships and physical links that connect various devices. These diagrams may also include illustrations and simplified design drawings, as needed.

A block diagram is another simplified representation of a circuit, showing only the most significant elements. It’s designed to furnish a broad overview of the function, structure, layout and operation of an electrical system. This format also serves as the initial reference for understanding more detailed schematic diagrams. Squares, rectangles, circles and symbols illustrate the components. Information about wire colors, terminal numbers, connectors, etc., are omitted to keep the diagram as simple as possible.

The schematic diagram shows a circuit and its elements in detail. By clearly depicting individual current paths, it also indicates how the electrical circuit operates. Most DIN schematic diagrams are current flow diagrams. They’re arranged from top to bottom, so we can clearly see how the current flows through the circuit. In a current flow diagram, a large block or several lines running across the top represent the fuse/relay panel. This is the positive side of the circuit. The numbered line across the bottom represents the chassis ground, completing the circuit to the battery.

Occasionally, a wire in a circuit will be continued in another current track. When this happens, a small box with a number inside will send you to the current track where the wire is continued.

Fig. 1 on page 38 is a schematic diagram of the gauge circuits on a Volkswagen. The lines across the top represent the positive feeds to the circuit. The numbers next to the bars define their wire gauge size and color. The individual gauges are mapped out in sequential order below, making it very easy to see how the current flows through the various sections of the circuit.

The diagram also includes information on terminal numbers, wire sizes and colors, connector sizes and a basic representation of the internal working of the gauges and sensors. The symbols used to define the components also conform to DIN specifications. A key explaining these symbols will often be included with the schematic diagram.

Even if you’re fairly familiar with a circuit on a given car, a schematic diagram will help you find the correct location of a ground terminal, or help you identify a specific pin number in a connector.

Another example of a current flow schematic diagram is shown in Fig. 2 (page 39). This diagram also explains the meanings of some of the letters and numbers in the diagram. The way the components and wires are situated in relation to one another in the diagram usually bears no resemblance to how they’re actually arranged on the vehicle.

Break this diagram down and you can see how it can work for you. Four things are needed to have a complete circuit: a source of power, wires or conductors of electricity, a load or a device that uses electricity and a ground. The load needs both voltage and ground. The schematic tells you where they come from, and where they need to go to reach the load terminals. It also tells you which switching devices are used to control the ON or OFF state of the circuit. The schematic diagram is laid out so you can quickly find the parts of a circuit and test them. For example:

*lf there’s no power at the coolant thermo switch, the diagram shows that fuse I is the source of power.

*If the fuse is good, the next step is to check the connections between the fuse and the thermo switch.

*The diagram shows two connections-terminal 87 at the relay and pin 6 of the green 10-point connector. Voltage testing at these points will help you determine where the break in the circuit is located.

Let’s look at one more schematic diagram, this time the backup light circuit in Fig. 3 (page 39). Again, it’s a current flow diagram, with all of the circuit components laid out end to end. All of the wires, connectors and other components are clearly labeled and identified. At the bottom of the diagram, note the circled numbers 7 and 8. These refer to the actual locations of the ground connections indicated in the diagram. An accompanying vehicle diagram shows you where the grounds are located.

The schematic diagrams used here are admittedly on the basic side. When the system involved is more complicated, several circuits may be included in the same diagram. Just remember, these more complicated schematic diagrams are assembled using the same basic building blocks and DIN conventions found in the simpler diagrams. When you’re troubleshooting a specific circuit problem, learn to home in on the part of the circuit that’s involved, and tune out all the clutter around it. If necessary, make a disposable copy of the diagram, then mark it up with colored pens or pencils until you understand how the circuit works.

DIN Relays

Suppose you’re diagnosing a relay in an electrical circuit. Perhaps the wiring diagram shows only a square box, with no information about what’s going on inside the relay. Or maybe you need to bench-test the relay or jumper the connector but can’t see the wire colors. If the vehicle uses DIN standards, the relay will provide you with information about its inner workings, just by looking at its terminal numbers. And for a more thorough explanation, many DIN relays even include a tiny schematic diagram on the outside of the housing.

Relays are electrically controlled switches. The switch inside the relay will be in one of two positions, depending on whether the electromagnetic relay coil is energized or deenergized. In basic relays, there’s one input and either one or two outputs. Relays are either normally open (NO) or normally closed (NC). In either case, the relay switch input is always connected to pin 30. Pin 30 not only designates the input to the relay switch, but in accordance with DIN standards, we also know that it’s connected to battery positive. The relay outputs on the other side of the relay switch are designated either 87, 87a or 876.

The two remaining relay terminals are connected to the relay coil. Applying current to the coil is what makes the relay close or open. According to DIN standards, pin 85 should be connected to ground (usually controlled by another switch) and pin 86 should be connected to battery positive (usually protected by a fuse). This one is not a hard and fast rule, apparently, as you may encounter relays where the polarities of terminals 85 and 86 have been reversed.

How does DIN pin number information help in the real world? By using pin information, you may be able to reduce the amount of time spent with locator manuals. When you remove a relay or look at a connector, you should be able to figure out how it works just by looking at the pin assignments.

Copyright Hearst Business Publishing Apr 2003

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