WARNING: Understanding the basics of electrical theory makes troubleshooting electrical equipment easier. Various electrical devices are used to diagnose electrical equipment malfunctions. Without understanding the basics, it will be difficult to understand measurement procedures.
Electricity is a flow of electrons, hypothetical particles that form the basis of electrical «substances». Compared to water flowing through a pipe, let's imagine that electrons are water. Since the flow of water can be measured (those. its characteristics), then the characteristics of the electron flow can also be measured. Current unit - ampere (A). An ammeter measures the amount of electricity flowing in a circuit per unit of time. Like water pressure is measured in units - Pa (Pascal), N/m2 (newton per square meter) etc., so the voltage of electricity is measured in volts (IN). When two wires of a voltmeter are connected to two points in an electrical circuit at different electrical potentials, current flows through the voltmeter and produces a voltmeter reading that indicates the difference in electrical potential between the two points in 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 the ohm, which is measured with an ohmmeter. An ohmmeter is similar to an ammeter, but it has its own voltage source, i.e. always gives the standard voltage. A real electrical circuit contains four main parts. This is the voltage source (generator or battery); a live wire that delivers a sufficiently high electrical voltage to the components that are connected to the circuit; load - lamps, electric motors, resistors, relays, ground wire that carries current back to a low voltage 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 earthed. In cars where the body is made of steel, it is used as the ground wire for most electrical wires.
Remember that for electrical measurements, the voltmeter is connected in parallel with the circuit being tested (without disconnecting wires) and the voltage difference between the two points where the voltmeter wires are located is measured; ammeter connected in series with load (the circuit is opened at one point and an ammeter is inserted there so that it becomes part of the circuit); and 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 wires.
For any electrical system to work, it must be a closed circuit, the voltage from the battery must-make a vicious circle. When electrical components are working, the voltage supplied to them by the battery is passed through the components, causing them to work (e.g. the lamp is lit), and then returned to the battery through the circuit ground. This ground is usually the metal part of the car that these circuit components are attached to.
It is possible that the easiest way to demonstrate what has been said is to connect the light bulb with two wires to the contacts of the battery. The battery has two terminals - negative and positive. If one of the wires that goes to the light bulb is connected to the negative pole of the battery, and the other wire to the positive pole, then you get a closed circuit. The current from the battery comes to the terminal, from the terminal through the wire it goes to the light bulb, passes through another wire and returns to the other terminal of the battery.
A normal automotive circuit differs from this example in two ways. First, instead of a wire carrying current back to the battery from the light bulb, the car uses the body of the car. Since the wire from the negative battery terminal is connected to the body and it is made of electrically conductive metal, 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 high current to operate also have relays in their circuit. Since these devices consume a large current, the thickness of the voltage supply wires must also be greater.
If the large wires ran from the consumers of the circuit to the control switch on the dashboard and then connected back to the consumer, then there would be a voltage drop in the circuit. Electromagnetic relays are used to prevent this potential voltage drop. 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 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 position «included» then a thin wire from a turnip is grounded, and the circuit is closed. If you were to disconnect the bulb in our example, connected with two wires from those wires, and then connect the wires again (you don't have to do this), then you would see sparks. Similar things happen when the wires supplying voltage to the consumers or the consumers themselves are grounded in a different way than provided by the circuit. Fuses are connected to the circuit to prevent damage. Since accidentally grounding wires from a voltage source causes the circuit to become closed, depriving components of voltage, this phenomenon is called a short circuit. Its main causes are: damage to the insulation of the wires, touching the bare wire of the metal parts of the car or a short circuit in the switch.