How to ring the wiring in a car with a multimeter: device, procedure for diagnosing a cable

People have long lived surrounded by electrical devices that imperceptibly enter the life of every person since childhood. Electronic watches, electric kettles, telephones, computers, cars are irreplaceable helpers in everyday life and at work. But sometimes devices break down and have to be checked and repaired. There is nothing difficult in this if you know how to use measuring instruments and know, for example, how to ring the wiring in the car with a multimeter or how to check the integrity of the electrical circuit.

General information

You don't need to be a professional electrician to find broken wires. It is enough to have measuring device - multimeter. The multimeter is a multifunctional measuring instrument with its own voltage source. The device can measure the voltage in the circuit, the magnitude of the current and the value of the resistance. Many multimeters are used to check the continuity of the connection in the circuit.

If a connection is found, the device beeps when there is a built-in speaker. This is where the term "call" came from. The device rings if there is a connection. And also a multimeter can indicate that there is no connection between the elements, and helps to determine a short circuit. With the help of the tester, all kinds of radio components are checked: resistors, transistors, diodes, relays, capacitors, and so on.

Conductor dialing based on Ohm's law for a section of an electrical circuit. Ohm's Law states that the resistance of an element is equal to the ratio of the applied voltage to the magnitude of the current in the electrical network section. Resistance is measured in ohms. A resistance of one ohm indicates that a current of one ampere flows through the conductor at a given voltage of one volt. Based on the calculated resistance data, conclusions are drawn about the results of the dialing.

That is, a certain voltage is set on the multimeter, and the current value is determined on the scale of the device and the resistance is calculated. In other words, a multimeter is a voltage source and an ammeter for measuring the current received.

Device device

Devices may vary in appearance, but fundamentally multimeters are divided into analog devices and digital devices.

Analog devices are already gradually being pushed out of the market by digital ones, but analog devices can still be found in the homes of many DIYers.

Such devices are equipped with an indicator screen with a scale and an arrow. The advantage of these models is the clarity of the display of measurements. The deviation of the arrow is visually easier to assess than the flickering of numbers on the electronic board of digital instruments. Often, when dialing, it is necessary to evaluate the approximate resistance values, or, in general, its presence or presence, therefore analog devices are suitable for most practical work.

Digital multimeters have more sophisticated electronics and digital displays. This type of device is used mainly in manufacturing and industry.

All multimeter housings have outputs for two probes. These are two wires in insulation, ending in needle-like metal nozzles. In some cases, special clips, the so-called "crocodiles", are put on the attachments. When choosing a device, special attention should be paid to the quality of the probes. The correctness of measurements depends on them.

The wires must be flexible with a strong solder and hold well in the device sockets. It often happens that outwardly spectacular probes are of unsatisfactory quality with poor technical characteristics.

Operating principle

For analog instrument type no own power supply required. Its principle of operation is the same as that of an ammeter, and the analog device works best in the range of radio waves and electromagnetic fields. There are induction coils inside the body of the device, and when the probes touch the conductor, a current begins to form in the coils. The created magnetic field deflects the indicator arrow by a certain angle. The magnitude of this angle depends on the strength of the current generated, and the arrow on the scale drawn indicates the value of the measurements.

In digital devices there is a textolite printed circuit board, on which there is digital microcircuitresponsible for processing the received data. For the operation of the circuitry and the screen, digital devices are powered by batteries or from an external power source.

Digital multimeters have less measurement error and are more accurate than their analog counterparts.

The front panel of the multimeter has a switch that selects the measurement mode. The switch sets the scale factor that determines the value on the scale of the device.

Analog instruments have two types of scale:

• Uniform indication.
• Logarithmic indicators.

The uniform scale is very sensitive to overloads, so the switch is first set to a large value for the scale factor, which is gradually reduced. The logarithmic scale is free from this drawback and has a range of values ​​from zero to infinity.

Thus, the main nodes of multimeters are:

• Display for showing measured values.
• Probe connectors and probes themselves.
• Switch for different modes and ranges.

Continuity of wires

It is imperative that before starting any measuring work, the serviceability of the tester itself is checked.

It happens that the measuring system itself is faulty. To check, the ends of the probes of the measuring device touch. If the device is functional, the indicator will display zero or deviate slightly. A small deviation indicates that the probes and terminals have their own low resistance.

If the multimeter has a beep, then the instrument is set to buzzer mode. This is done by setting the switch to the corresponding icon on the tester body.

The probes are brought up to the ends of the part to be checked.

Possible options for tester behavior:

• Zoom will be heard if the wiring is intact.
• The cable may be functional, but it is very long. In this case, the resistance of the conductor will be much greater than something at which the sound signal is triggered. The display will come to the rescue and display the resistance value.
• If the indicator shows a unit, then the resistance value is higher than the permissible range of the multimeter scale. It is necessary to switch to another range and repeat the measurement.
• In the event of a wire malfunction, the multimeter will not perform any action.

When measuring with a multimeter, the human body must not be allowed to come into contact with probes and wires where there is no insulation.

Finding faults in the car's electrical circuit

If some unit does not work in the car, then first of all it is necessary to check the electrical circuit. There is no particular difference between how to ring out different wires with a multimeter in different cars, except for the high-voltage cable.

First, make sure that there is voltage in the circuit of the inoperative unit:

• The multimeter is configured with a switch to measure voltage.
• The multimeter probe is connected to the mass of the car or to the minus of the battery. A feature of the supply pair in the car is that the negative cable is either very short or absent at all.
• The remaining probe touches the supply cable. The wire must be disconnected from the terminal of the device.

If the tester's indicator shows the presence of voltage, then the wire is intact. By analogy, all the wires of the node are called. If the wire is damaged, the scale of the multimeter shows zero.

It must be borne in mind that voltage is supplied to some parts of the car only when the ignition key is on.

At the end of the voltage check, the current strength is checked. The device is transferred to the ammeter mode, the switch is in the measuring range up to ten amperes. All devices of the car must be turned off, and the tester must be correctly connected to the electrical network of the car. For this, a multimeter is connected between the positive contact of the battery and the unit under test. The screen of the device should display the found value of the current strength, it should correspond to the consumption of the constantly switched on devices of the machine. If the current strength exceeds the norm, a conclusion is made about its leakage.

In this case, start checking the devices that are not included in the standard equipment of the car, and the places where the wiring is part of the moving mechanical assemblies.

Experienced craftsmen identify areas with a drop in current strength, focusing on the readings of a multimeter with fuses removed alternately. Then check the sparking on the contacts.

If a misbehaving wire is detected, it is ringed to check for continuity, and then its resistance is measured.

One of the answers to the question of how to ring the wires with a multimeter is to measure the resistance of each of the wires in the node. The rating is applied to the braid, and the tester is connected to the wire in ohmmeter mode. Typically, the range of resistance values ​​for automotive wiring ranges from 3.5 to 9.9 kOhm. The difference between the measured element and the norm should not be more than four kilo-ohms.

Checking the armored wire

The vehicle's power supply pairs consist of a high-voltage wire for the ignition system. Before ringing the power wire with a multimeter, carry out visual diagnostics with the engine running. When the candles are lit, the voltage reaches several thousand volts.

Therefore, when high-voltage insulation breaks down, a spark occurs at a distance of three to five millimeters from the damaged area. In this case, if the insulation is damaged, then sparking is accompanied by a breakdown to the engine, and the spark plug does not perform its function. If the diagnosis is carried out indoors or on a dark street, then the breakdown is clearly visible. The charge from the faulty area can heat up the insulation until it burns out.

The cause of the malfunction may be damage to the contact assembly. In this case, the resistance of the central core increases. During corrosion, due to thinning, some wires in the harness break, and the high resistance prevents the amperage from reaching the required level. Voltage, in turn, is not applied to the spark plug electrodes.

Checking a high voltage cable is different from ringing the wires with a multimeter, because the current in the cable is small. This is due to the very high voltage that flows through the power wire. Therefore, such wires have thick insulation and a small core diameter. In buzzer mode, the multimeter will not distinguish a whole wire from a damaged one.

In this case, the resistance is measured. To begin with, visually inspect the connection of contact groups. According to statistics, breaks most often occur precisely at the points of contact.

Then they clean the contacts with an emery cloth from corrosion and an oxidizing layer in order to avoid measurement errors. The multimeter is switched to the resistance measurement mode with a measurement range of up to ten kOhm. Hands should not come into contact with wires and contacts. An intact armored train has a resistance of 3.5 kOhm to 10 kOhm. In any case, it is best to find the resistance data in the technical documentation and compare with the obtained ones. The difference should not be more than ten percent.

If there is no instruction at hand, then several wires are ringing in turn. The spread in the resistance values ​​of each of the elements should not be more than two or three kilo-ohms.

Directly during the measurement, when the cable is twisted, stretched or bent, the resistance should not "jump".

It is best to test any wires, harnesses, especially in a car, if an electrical and circuit diagram is present. Otherwise, it is difficult to figure out where which wire is in the bundle.

After learning the basics of measuring with a multimeter and mastering the work by the elimination method, anyone can independently diagnose and fix a fault in the wires.