The first step should always be to check the fuse if the electrical assembly being tested is protected by it. The purpose of the fuses is given on the cover of the fuse box.
A defective fuse must be replaced and it must be checked whether the new fuse blows immediately after switching on the consumer of electricity; in this case, it is necessary to first find the cause of the malfunction. As a rule, the problem is a short circuit. This means that in some place, sometimes in the electrical device itself, the points of mass are bridged (-) and positive potential (+).
Second step. If, with a good fuse, the incandescent lamp does not light, or, for example, the electric motor does not rotate, then you need to check whether the power is supplied.
Incandescent lamp test
1. Unscrew the lamp and inspect it. If the filament is burned out, or the glass bulb does not sit tightly in the base, then such a lamp must be replaced.
To make sure that the lamp is working, proceed as follows: connect two wires directly to the battery poles and attach them to the lamp. Polarity does not play any role in this. One of the wires goes to the current contact, and the other to the lamp socket. If the lamp still does not light up, replace it. But in this case, you need to be sure that the contacts of the lamp and the cartridge are not covered with corrosion. If necessary, treat corroded or bent clamps and terminals with abrasive paper and restore reliable contact.
2. Replace the light bulb and turn it on if it is good. If the light does not light up, use a test light to check the power supply. To do this, connect a test light to «mass» (-). This means that one of the test lamp contacts must be securely attached to the engine housing (pure metal) or directly to the negative pole of the battery. Other contact (+) touch the power plug or the power cable directly. If the control lamp lights up, and the lamp under test is still off, then this means that the connection between the lamp and the «weight» (-). To check this, attach an auxiliary wire connected to the car body to the lamp socket. The lamp should now be on.
If there is no voltage on the supply wire, that is, the control lamp does not light up, then it is very likely that the switch is faulty. In this case, it is necessary «ring out» switch.
Checking electric motors
An increasing number of functions related to ensuring the comfort of the car are performed by small electric motors. They actuate, for example, power windows, sunroof or central locking.
Each electric motor is turned on, if necessary, using a separate switch, usually manually.
3. Check the fuse for the relevant motor. Replace fuse if necessary.
Attention! The electric motors for the power window and the sunroof are equipped with automagic fuses that turn off when overloaded and turn on again after a while. Eliminate the cause of the overload before restarting. This may be caused by frost on the windows or dirty window guides.
If the fuse blows again immediately, this indicates a short circuit.
To establish unequivocally whether the defect is related to a malfunction of the electric motor, connect it with auxiliary wires (with a cross section of 2 mm) directly to the battery or the appropriate leads from the battery. In this case, polarity must be observed. In case of doubt about the correctness of the selected polarity, it can be checked using the switching diagram. But in this case, you will have to remove the electric motor.
All electric motors of the car are powered by on-board voltage (12-14 Volt). If the motor runs normally after applying power through the auxiliary wires, it means that it was not powered. If the motor rotates too slowly or intermittently, wear of the graphite (coal) brushes. In this case, the motor brushes must be replaced.
If the engine is running, then, guided by the electrical diagram, determine which wire supplies voltage to it, if the ignition is on and the switch is on.
4. Check up a wire of food of the engine by means of a control bulb. Since the motors consume a lot of current, you can use a conventional test light. The connecting wires of this tester have sharp probes that can pierce the wire insulation, making it easy to check the voltage.
If voltage is not supplied to the motor, then this indicates a power failure. It is necessary to find and eliminate the malfunction according to the principle diagram. Due to the high current consumption, electric motors usually have an additional switching relay.
5. Check the switch if no fault is found.
If the wire is broken, then it is more advisable to lay a new one, since it can be difficult to localize the place of the wire break.
Switches - current flow test
Most consumers of onboard electricity are turned on and off manually using a switch. In addition, there are automatic switches. These include, for example, the engine oil pressure sensor and the brake fluid level sensor.
The switch is mainly used to close and open an electrical circuit. There are switches that open the connection to «weight» (-), as well as switches that break the connection with a positive potential (+).
Checking Light Switches and Motors
6. Remove the appropriate switch. Simple switches have only two leads for connecting a wire. In this case, one output should always have (+), and on the other output, a plus appears after switching on. There are also switches with multiple terminals. For these switches, you should find out from the diagram which terminal should be energized. Turn on the ignition first, if necessary.
7. Check up tension by means of a control bulb. If the control lamp lights up, turn on the switch and check the voltage at its output terminal. If there is voltage, then it is safe to say that the switch is working. If there is no voltage at the input terminal, this indicates a break in the supply wire. It is necessary to check the power supply according to the electrical circuit, and, if necessary, lay a new wire.
Checking the sensors-switches
They are switches. for example, sensors for brake fluid, engine oil and coolant level warning lights.
8. Connect a device to the two terminals of the sensor plug to «ringing» (test light or ohmmeter), by disconnecting the sensor plug.
Attention! Sensors screwed into the cylinder block usually do not have a wire «masses» (-), so their attachment to «mass» (-) occurs through the cylinder block, on which the body of the sensor itself closes.
When closed (included) sensor, the device should show the passage of current. For such «ringing» It's best to use an ohmmeter. When the sensor is closed, it should show 0 ohms, and when open, it should show ∞ ohms (infinite resistance).
The operability of switches such as a coolant or brake fluid level sensor can be most quickly checked by disconnecting the power wire from it with the ignition on, which is then connected to «mass» (-), for example, to the cylinder block. If now the light on the instrument panel works, then the sensor is faulty.
Relay test
Many electrical circuits incorporate relays. The switching relay works like a switch. For example, in order to turn on a consumer using a manual switch, you must manually press it or move it to the desired position. Relay in this case «receives an order» supply power to the appropriate consumer. Of course, the voltage from the battery to the consumer could also be applied directly through the switch. But in the electrical circuit of all devices that consume high current, a relay is included as an intermediate link so as not to overload the switch, or to shorten the current path.
Checking switching relays
When the corresponding consumer is turned on, the voltage supplied to the relay closes its electrical circuit. The magnetic coil inside the relay attracts the contact, thus completing the circuit «working» current. «Worker» current flows from the relay to the consumer.
The easiest way to test a relay is to replace it with a known-good relay. That's how they do it in workshops. But since the motorist does not always have spare relays on hand, the following approach is recommended when checking them.
9. Remove the relay from the holder.
10. Turn on the ignition and the appropriate switch.
11. Check with a voltmeter if voltage is supplied to the terminal (+) on the relay holder. To do this, connect the tester to «mass» (-), and carefully place the other contact rod on the terminal (+). If the tester does not register voltage, look at the circuit diagram for an open circuit from the positive pole of the battery to the terminal (+) relay holder.
12. Make a jumper from a piece of insulated wire, exposing its ends.
13. Connect this jumper to the terminal (+) on the relay holder (voltage is supplied here constantly from the battery) with relay closing contact. This technique does almost the same thing that a working relay should do. The location of the terminals on the relay holder can be determined by the markings on the contacts or on the relay itself.
If the corresponding network consumer works with the jumper installed, then it can be assumed that the relay is faulty.
If the consumer does not work in this case, find out if the connection of the consumer is working properly on «mass» (-) car. Then, according to the circuit diagram, find and eliminate an open in the circuit from the relay terminal to the current consumer.
14. Install a new relay if necessary.
Attention. If the relay functions intermittently, then the problem, as a rule, should be sought in the relay itself. Sometimes there is a so-called gluing of the relay contact, as a result of which it does not open, although the rest of the relay works flawlessly. If this problem is detected, you just need to knock on the relay housing. If this relay closes again, replace this relay with a new one.
Plugs - Disconnect
Attention! When disconnecting the plug, pull not by the wire, but by the detachable block, depressing the locking leash.
Most car electrical system plugs are mounted in a holder.
In order to remove the plug from the holder, it is necessary to remove the latch tab on the housing. To disconnect the plug, press on the locking latch. For some plugs, the leash of this latch must be lifted up.
Stoplight - check
15. Check up bulbs of lanterns of stoplights and if necessary replace them.
16. Check the fuse in the fuse box if the correct brake lights do not come on.
17. Check the brake light switch if the bulbs and brake light fuse are OK. The brake light switch is located on the brake pedal bracket. When you press the brake pedal, the pressure finger comes out of the switch. The switch contact closes and the brake lights come on.
18. Remove the cover above the brake pedal bracket and disconnect the brake light switch plug.
19. Turn on the ignition.
20. Bridge both contacts of the switch plug with a piece of wire. If the brake lights come on, the switch is defective and should be replaced.
Rear window heater - check
When the heated rear window is turned on, the icing or fogging of the rear window should disappear after a while.
21. Check the fuse first if the heater is not working.
22. Check the fit and condition of the contacts of the rear window heater power plugs, if the fuse is in order. If necessary, clean the contacts of the plugs.
If the heater still does not work, then check the wires and make sure they are not broken.
If the wires are in order, then check that the heater filaments are not damaged. To do this, wrap the tip of the tester with a wide strip of foil, with which you touch the heating filaments, starting the engine and turning on the heater. Check the thread by touching it approximately in the center. The voltage of a healthy filament is about 6 V. If the voltmeter registers a voltage of 10 V or 0 V, then the filament is broken.
If the heating filaments are broken, they can be repaired with a commercially available silver-based conductive lacquer. To do this, clean the damaged area with a soft cloth.
23. Paste the damage on both sides with adhesive tape and apply conductive varnish with a brush.
24. Let the varnish dry for 24 hours at +25°C. If necessary, you can use a hairdryer. At a temperature of +150°C, the varnish dries in 30 minutes.
Attention! Do not turn on the rear window defroster until the varnish is dry. Do not use gasoline or other solvents on damaged thread.
Glass cleaner motor - check
The windshield wiper motor is located in the fairing box under the windshield. To check the electric motor, it is necessary to remove the fairing. Therefore, before checking the electric motor itself, check its fuse.
25. Check the purifier fuse and replace it if it is blown.
26. Disconnect the multi-pin motor plug.
27. Use auxiliary wires to supply voltage to the motor contacts from the battery.
If the motor is OK, then it should rotate. Otherwise, the motor must be replaced.
Turn signal breaker - check
The cycles of intermittent, flashing light of the lamps of the front and rear lights when turning the car and the intermittent light of the alarm are created by the electromagnetic relay-interrupter of the direction indicators. If the rhythm of the interruption of the direction indicator light on one side of the car has a higher frequency than on the other, then the cause of this is a burnt out lamp or a wire break on this side.
If the incandescent lamp is working, then in this case, first of all, you should check the fuse for the turn signal breaker.
In other cases, the cause of the malfunction lies in the breaker itself.