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Common Electrical Circuit Symbols: Symbols are used to represent various automotive electrical components. These are referred to as schematic symbols, and are used extensively in automotive service manuals to aid in diagnosing electrical problems. Although there are many electrical symbols used in circuit diagrams, we will look at some of the more common symbols.

 
 For the battery symbol, the long lines represent positive plates and the short line represents negative plates. each pair (one long and one short) represents one cell. Since we are referring to the 12-volt automotive battery, there are six cells. Each cell has the potential of creating approximately 2.2-volts, therefore, the six cells provides a total of 13.2-volts (even though we refer to it as a 12-volt battery).

 

 As you are probably aware, switches are used to turn an electrical device ON or OFF. Technically speaking, the switch is use to close (turn off) and open (turn on) an electrical circuit. This will be easier to understand when we study circuits.

 

 The bulb (light bulb) symbol can represent any type of light bulb (headlight, taillight, etc). The squiggly line inside the circle represents the filament found in typical incandescent light bulbs. One end of the filament will be connected to the positive side of the circuit and the other end to the negative (ground) side of the circuit.

 

 The ground symbol represents a electrical connection to the metal body or frame of the vehicle. In turn, the negative cable of the battery is connected between the negative battery terminal and the body/frame of the vehicle. Since the steel used in the construction of the body/frame will conduct electricity, a separate wire is not needed to complete the circuit.

 

 The fuse is a circuit protection device. If the current exceeds the maximum rating for the circuit, the fuse element melts, thereby opening the circuit. Without the fuse to protect the circuit, the wiring itself would overheat, melt, and possibly start a fire.

 

 A circuit breaker is also a circuit protection device. Unlike a fuse, however, the circuit breaker resets once the overload condition goes away. Circuit breakers are typically used in safety related circuits, such as headlights and windshield wipers.

 

 A fixed resistor is a electrical device that is used to reduce current flow. Looking at it in terms of a hydraulic circuit, it is a flow restriction. Resistors reduce electrical energy by converting some of it into heat energy. The heating elements in a toaster are resistors.

 

 A variable resistor value can be changed by moving a sliding contact. An example of its use would be to vary the brightness of lights, such as in the instrument panel dimming circuit. The most common use today is for sensors that provide information to the various computers. Such an example would be the fuel level sensor in the fuel tank.

 

 A dot at the intersection of wires is a permanent connection point, or splice.

 

 When creating wiring diagrams, it is not possible to draw all of the lines that represent wires in such a way as to not cross over. If there is no dot at the intersection of the lines, then those wires are not connected.

 

 This symbol represents a male-female connector. If it a one piece multiple wire connector (harness), the connectors will be surrounded by a box.

 

 A relay is a remote controlled switch. The relay coil is an electromagnet that, when energized by applying voltage to it, will magnetically pull a spring-loaded switch to another position. In the schematic symbol, the broken line between the relay coil and the switch indicates that the coil affects that switch. Not all relay symbols will have the broken line. In the schematic symbol, the switch is typically shown in its spring-loaded, or deenergized position. A relay allows a small current (through the coil) to control a much larger current carried by the switch.

 

 This is the symbol for a dc. (direct current) electric motor. The direction the dc. motor shaft rotates depends on the polarity of the connection to the power source.

 

 This is the symbol for a dc. (direct current) generator.

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