Under the concept of voltage in the car, as a rule, we mean the voltage of the battery. This is a constant voltage of about 12 V. The battery voltage depends on the charge and the outside temperature. It can be from 10 to 13 V. The generator creates an on-board network voltage of about 14 V at medium speeds.
The current strength is indicated on the back of the fuses and indicates the maximum current that can pass the circuit without burning the fuse and thereby disconnecting the circuit.
The resistance depends on the following factors: wire cross-section, conductor material, current consumer, etc. For example, the resistance in high voltage wires should not be too high: otherwise the ignition spark on the spark plugs will not be strong enough to ignite the air-fuel mixture and the engine does not start or runs intermittently.
For measurements, so-called multi-purpose measuring instruments are commercially available. They combine a voltmeter, ammeter and ohmmeter in one device.
Multi-purpose devices are intended for cars, with the help of which engine speed, ignition timing and, in addition, voltages up to 20 V can be measured. When measuring resistance, the device is usually limited to the kiloohm region of 1–1000 kOhm.
If it is necessary to check only the presence of voltage (IN), then for this it is enough to use a control lamp. This only applies to circuits that do not have electronic components, as they are extremely sensitive to high currents. Under certain conditions, the units can even be disabled by connecting a warning lamp.
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