Many people think that understanding circuit diagrams is the most difficult part of learning electrical systems, because circuit diagrams are schematic diagrams of some components, and they simply don’t understand what these diagrams express. Moreover, a circuit diagram usually has dozens or even hundreds of components, and their connections cross vertically and horizontally, and their forms vary widely. Beginners often don’t know where to start and how to understand it.
In fact, the truck circuit itself has a strong regularity. No matter how complicated the circuit is, it can be found through analysis that it is composed of a few unit circuits. It seems that although there are only a dozen or twenty or thirty kinds of blocks for children to play with, they can be built into dozens or even hundreds of flat figures or three-dimensional models in the hands of children.
In the same way, no matter how complicated the circuit is, it can be found after analysis that it is also composed of a few unit circuits. Therefore, beginners only need to be familiar with the common basic unit circuits first, and then learn the skills of analyzing and decomposing circuits, it should not be difficult to understand the general circuit diagrams. So in this issue, let’s briefly introduce the schematic representation of common components on circuit diagrams:

The following electrical symbols are standard symbols and are not limited to trucks.

## Wires and connections: ## In addition to the connections between various wires and resistors in the wiring diagram, there are also some electrical connections: ## And various sensors and control switches: In the circuit diagram of Volvo Trucks, we will see that each component is expressed in the form of letters + numbers, such as A01, which represents the center of the fuse and the relay. It is impossible for us to remember what the parts represented by so many codes are, but we can know what kind of part this part is through the first letter, so as to know its working process or roughly judge its position on the car.

## The following is a summary of the meaning of the letters:

A: Control unit
B: Sensor
E: light bulb
F: Fuse
G: Generator
H: Horn
K: Relay
M: Electric motor
R: resistance and heater
S: switch
U: Transformer
V: Diode
W: Antenna
X: plug
Y: Solenoid valve

## The letters on the wire indicate the color of the wire: ## The number on the circuit diagram indicates the cross-sectional area of the circuit, in square millimeters. Note that the cross-sectional area of the core does not include the insulating layer.