Reading electrical diagrams

In a passenger car, depending on the configuration, up to 1000 meters of wires are laid to power all consumers of electricity (headlights, radio, etc.).

If you need to find a malfunction in electrical equipment or install additional electrical units, then you can’t do without a circuit diagram, since it reflects the current characteristics and wire connections. Each electrical circuit must be closed, otherwise the electric current will not flow. For example, just having voltage applied to the positive terminal of the headlight is not enough unless the circuit is simultaneously closed to «mass» (-).

Therefore, the negative pole of the battery (-) also wired to the body. Sometimes such accession to «mass» (-) is not enough, and one or another consumer of electricity has a separate wire connecting it to the car body. Such wires usually have brown insulation. Switches, relays, fuses, measuring instruments, electric motors and other electrical components and parts can be combined in separate circuits. So that they can be connected correctly, each contact has a corresponding designation.

To facilitate the perception and understanding of the wire connections in the diagram, each wire is placed vertically next to each other and is numbered.

In the diagram, the vertical lines at the top enter into a box that usually has a gray background. This rectangle symbolizes the relay box with fuses and the connection to the positive potential. In addition, the relay block also has its own internal connection on «mass» (-) (terminal 31). The thin lines in the box show how the circuits are connected to each other within the block. At the bottom, the chain ends with a horizontal line, which symbolizes accession to «mass» (-).


If an electric circuit is interrupted by a square with a number inside it, then this number indicates the further path of the current in the circuit after the connection.

When using circuit diagrams, it is most rational to proceed as follows:

• First, find the corresponding part in the legend. They are listed on the corresponding diagram. In the left column next to the name of the part in the form of a number, the corresponding designation of a letter and one, two or three digits is given, under which this part is indicated in the diagram.
• The right column shows the name of the part.