WARNING: Understanding the basics of electrical theory makes troubleshooting electrical equipment easier. Various electrical instruments are used to diagnose electrical equipment problems. Without understanding the basics, it will be difficult to understand the measurement procedures.
Electricity is the flow of electrons, 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), the characteristics of the flow of electrons can also be measured. The unit of measurement for current is the ampere (A). An ammeter measures the amount of electricity flowing in a circuit per unit of time. Just as water pressure is measured in units of Pa (Pascal), N/m² (Newton per square meter), etc., so 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 that shows the difference in electrical potential between these two points of the electrical circuit, i.e. voltage. As the voltage in a circuit increases, so will the current, 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 by 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 the voltage source (generator or battery); a live wire that supplies a sufficiently high electrical voltage to components that are connected to a circuit; load - lights, motors, resistors, relays, ground wire that carries current back to the low voltage source. In such a circuit, there is resistance between the point where the live wire connects 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 wiring.
Remember that when making electrical measurements, the voltmeter is connected in parallel to the circuit being tested (without disconnecting the wires) and the voltage difference is measured between the two points where the voltmeter wires are located; the ammeter is connected in series with the load (the circuit is broken at one point and the 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 leads.
For any electrical system to work, it must be a closed circuit, meaning the voltage from the battery must make a closed circle. When electrical components work, the voltage coming to them from the battery passes through the components, causing them to work (like a light bulb), and then returns to the battery through the ground of the circuit. This ground is usually the metal part of the car that these components of the circuit are mounted to.
Perhaps the easiest way to demonstrate this is to connect a light bulb with two wires to the terminals of a battery. There are two terminals on a battery - negative and positive. If one of the wires leading to the light bulb is connected to the negative terminal of the battery, and the other wire to the positive terminal, a closed circuit is created. Current from the battery goes to the terminal, from the terminal through the wire goes to the light bulb, passes through the other wire and returns to the other terminal of the battery.
A normal car circuit 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 wire from the negative terminal of the battery is connected to the body, and the body is made of metal that conducts electricity, the car body can serve as a ground wire to complete the circuit. Second, most car circuits contain switches to connect and disconnect consumers.
Some electrical components that require a lot of current to operate also have relays in their circuit. Since these devices consume a lot of current, the thickness of the supply wires should also be larger.
If large wires were to run from the loads in the circuit to a control switch on the dashboard and then reconnected to the load, 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 load. A normal relay is open (open) preventing current from flowing through the circuit. In addition, thin wires are run from the relay to the load'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 complete. If you were to disconnect the light bulb in our example, which was connected by two wires to these wires, and then reconnect the wires (this should not be done), you would see sparks. This type of thing happens when the wires that supply voltage to the loads or the loads themselves are grounded differently than intended by the circuit. Fuses are included in the circuit to prevent damage. Since the accidental grounding of wires from a voltage source causes the circuit to become closed, depriving components of voltage, this phenomenon is called a short circuit. The main causes are: damage to the insulation of the wires, contact of the bare wire with metal parts of the car, or a short circuit in the switch.
(The original article was published on: MITSUBISHIMAN)