How to Use Wiring Diagrams

PROCEDURE

If it is necessary to locate a fault in the electrical equipment or to install additional electrical consumers, it is very difficult to do this without the help of wiring diagrams. Wiring diagrams show the flow of current, i.e. the connections between electrical circuits. Since the vehicle body is the "ground", the negative battery cable is connected to the body. Most electrical consumers are connected to "ground" by a brown wire. Individual circuits may contain switches, relays, fuses, measuring instruments, electric motors or other electrical devices and components. To ensure that these components are connected correctly, the terminals are marked accordingly. To make it easier to find the required wires on the wiring diagrams, certain current paths are arranged vertically next to each other and numbered. The vertical lines usually end at a shaded field. This field symbolizes the relay and fuse box and therefore the positive connection point of the electrical circuits. The relay board also has an internal connection to "ground" (terminal "31"). The thin lines in this field indicate which circuits are switched and how, using the corresponding relays. At the bottom, the current path ends at a horizontal line, which indicates the connection to "ground". The ground connection is usually made directly through the body; however, it may also be made by a wire running from a point on the body. If a wire is interrupted by a square with a number, the number indicates the current path on which the circuit continues on other diagrams. When using wiring diagrams, it is recommended to first find the required component in the list (next to or below the diagram), for example the fan switch. To the left of the component name, the number of the corresponding current path is indicated; this number is repeated on the diagram and at the bottom on the horizontal line. To make wiring diagrams easier to read, it is necessary to learn the letter and graphic symbols for components. To identify a component precisely, numbers are added to its letter designation. Internal connections are shown inside the symbol. They show how relays and other components are connected to each other. The number in the black square indicates the position of the relay on the relay and fuse box board. For example, if the designation "17/87" is shown, then "17" is the terminal number on the relay board, and "87" is the terminal number on the relay or control unit. Terminal designations comply with the 01M standard. Terminal "15" receives power through the ignition switch. Current flows through these circuits only when the ignition is switched on. Terminal "X" also carries current only when the ignition is switched on; however, it stops flowing at the moment the starter is engaged. This ensures that the full battery power is available when starting the engine. All the main electrical consumers are located on this circuit. The low beam filaments of the headlamp are also powered from this terminal. Thus, when the high beams are on and the ignition is off, the system automatically switches to the parking lights. Terminal "30" is permanently live from the battery. Terminal "31" is connected to "ground". Ground wires are usually brown. On wiring diagrams, numbers such as 1.5 are shown next to individual wires. The number indicates the wire cross-section in mm². Since wires of the same color are sometimes used in different circuits, it is recommended to check the wire combinations at the corresponding connection points. Wires that are joined by single- or multi-pin connectors have, in addition to the letter designation of the connector ("T"), an additional designation. Example: "T2p" designates a two-pin connector, "T32/27" designates pin 27 of a 32-pin connector. All electrical consumers and switches are shown in the switched-off position on the wiring diagrams.