Note: Understanding the basics of electrical theory makes troubleshooting electrical equipment easier. Various electrical devices are used to diagnose electrical equipment faults. Without understanding the basics, it will be difficult to understand measurement procedures.
Electricity is the flow of electrons, the hypothetical particles that make up the basis of electrical "stuff." In comparison to water flowing through a pipe, imagine that the electrons are the water. Since the flow of water can be measured (i.e. its characteristics), then the characteristics of the electron flow can also be measured. The unit of measurement of current is the ampere (A). An ammeter measures the amount of electricity flowing in a circuit per unit of time. As well as water pressure is measured in units - Pa (Pascal), N/m² (newton per square meter) etc., and the voltage of electricity is measured in volts (V). When two leads of a voltmeter are connected to two points of an electrical circuit with different electrical potential, current flows through the voltmeter and gives a voltmeter reading, which shows the difference in electrical potential between these two points of the electrical circuit, i.e. voltage. As the voltage in the circuit increases, the current will also increase, which will depend not only on the voltage, but also on the resistance of the circuit. The unit of resistance is Ohm, which is measured with an ohmmeter. An ohmmeter is similar to an ammeter, but has its own voltage source, i.e. it always gives a standard voltage. A real electrical circuit contains four main parts. This is a source of tension (generator or battery); a live wire that supplies a sufficiently high electrical voltage to components that are connected to a circuit; load - lamps, motors, resistors, relays, ground wire that carries current back to the low voltage power source. In such a circuit, there is resistance between the point where the live wire is connected to the load and the point where the load is grounded. In cars where the body is made of steel, it is used as a ground wire for most electrical wires.
Remember that when making electrical measurements, the voltmeter is connected in parallel to the circuit being tested (without disconnecting wires) and the voltage difference between the two points where the voltmeter wires are located is measured; the ammeter is connected in series with the load (the circuit is broken at one point and an ammeter is connected there so that it becomes part of the circuit); the ohmmeter is powered by its own source, so all power sources in the circuit must be turned off and the part of the circuit to be measured must be connected to one of the ohmmeter leads.
For any electrical system to work, it must be a closed circuit, i.e. the voltage from the battery must make a closed circle. When electrical components operate, voltage comes from the battery and passes through the components, causing them to operate (for example, the lamp is glowing), and then returns to the battery through the circuit ground. This ground is usually the metal part of the vehicle to which these circuit components are mounted.
Perhaps the easiest way to demonstrate this is to connect a light bulb with two wires to the battery terminals. There are two contacts on the battery - negative and positive. If one of the wires leading to the light bulb is connected to the negative pole of the battery, and the other wire to the positive pole, a closed circuit will be created. Current from the battery goes to the terminal, from the terminal through a wire goes to the light bulb, passes through another wire and returns to the other terminal of the battery.
A normal car wiring diagram differs from this example in two ways. First, instead of a wire that carries current back to the battery from the light bulb, the car uses the car body. Since the negative battery terminal wire is connected to the car body, which is made of a metal that conducts electricity, the car body can serve as a ground wire to complete the circuit. Secondly, most automotive circuits contain switches to connect and disconnect consumers.
Some electrical components that require a lot of current to operate also have a relay in their circuit. Since these devices consume a lot of current, the thickness of the supply wires must also be larger.
If large wires were run from the circuit consumers to the control switch on the instrument panel and then connected back to the consumer, there would be a voltage drop in the circuit. To prevent this potential voltage drop, electromagnetic relays are used. Thick wires are connected from the battery to one side of the relay and from the other side of the relay to the consumer. Normal relay is open (open), preventing current from flowing through the circuit. In addition to this, thin wires run from the relay to the consumer's control switch.
When the control switch is turned to the "on" position, the thin wire from the relay is grounded and the circuit is closed. If you were to disconnect the light bulb from our example, connected by two wires from these wires and then connect the wires again (there is no need to do this), then you would see sparks. Such things happen when the wires that supply voltage to consumers or the consumers themselves are grounded differently than provided for in the circuit. To prevent damage, fuses are connected to the circuit. Because accidentally grounding wires from a voltage source causes the circuit to become shorted, depriving components of voltage, this phenomenon is called a short circuit. The main causes are: damage to the wire insulation, contact of bare wire with metal parts of the car, or a short circuit in the switch.