The electrical equipment of the car is made according to a single-wire circuit: the negative conclusions of the sources and consumers of electricity are connected to the "mass"
The function of the second wire is performed by the car body. The electric circuits of the engine management system are made according to the multi-wire scheme and are connected to the car"s "ground" only through the electronic control unit
Consumers are powered by a battery (when the engine is not running) and a generator (when the engine is running).
To switch the main circuits of the car, a combined ignition switch (lock) is used, consisting of a contact part and a mechanical anti-theft device with a lock.
For ease of operation and viewing, the diagrams are divided into sections of the circuit.
Carry out any work on the vehicle"s electrical equipment only with the battery disconnected.
Disconnect or connect the battery only when the ignition is off.
When checking the circuits of electrical equipment, it is forbidden to short the wires to ground (check the health of the circuits “for a spark”), as this can lead to failure of electrical equipment elements. It is forbidden to use fuses that are not provided for by the vehicle design or designed for a higher current, and also to use wire instead of fuses.
When replacing fuses, do not use screwdrivers, as this can lead to a short circuit in the electrical circuits.
It is forbidden to disconnect the battery while the engine is running in order to avoid damage to the voltage regulator and elements of the vehicle"s electronic equipment.
When carrying out electric welding work on a car, it is necessary to disconnect the wires from the terminals of the battery, generator and controller.
A typical electrical circuit may include a main electrical element, various switches, relays, electric motors, fuses, fuses or circuit breakers related to this element, wiring and connectors that connect the main element to the battery and body ground.
Before you begin troubleshooting any electrical circuit, carefully study the relevant diagram in order to understand its functional purpose as clearly as possible.
The circle of troubleshooting is usually narrowed by gradually identifying and eliminating normally functioning elements of the same circuit.
With the simultaneous failure of several elements or circuits, the most likely cause of failure is the blown out of the corresponding fuse or a violation of contact with the "ground" (different circuits in many cases can be closed to one fuse or ground terminal).
Electrical equipment failures are often due to the simplest causes, such as corroded connector pins, blown fuses, blown fuses, or broken relays. Visually check the condition of all fuses, wiring, and circuit connectors before proceeding to a more detailed check of the health of its components.
When using diagnostic tools for troubleshooting, carefully plan (according to the attached wiring diagrams) where and in what sequence the tool should be connected in the loop for the most effective troubleshooting.
Basic diagnostic tools include an electrical circuit tester or voltmeter (you can also use a 12-volt test lamp with a set of connecting wires), an open circuit indicator (probe) that includes a lamp, its own power source and a set of connecting wires.
In addition, you should always have in the car a set of wires for starting the engine from an external source (the battery of another car), equipped with crocodile clips and preferably an electrical circuit breaker. They can be used for shunting and connecting various elements of electrical equipment when diagnosing a circuit. As already mentioned, before proceeding with the circuit test using diagnostic equipment, determine the connection points from the diagrams
Checks for the presence of supply voltage are carried out in case of an electrical circuit failure
Connect one of the electrical circuit tester wires to the negative battery terminal or make good contact with the vehicle body. Connect the other tester lead to the connector pin on the circuit under test, preferably closest to the battery or fuse.
If the tester"s control lamp lights up, there is supply voltage on this section of the circuit, which confirms the health of the circuit between this point in the circuit and the battery
Proceeding in the same way, explore the rest of the chain. Detection of a supply voltage failure indicates the presence of a malfunction between this point in the circuit and the last one previously checked (where the supply voltage was)
In most cases, the cause of the failure is loosening of the connectors and damage to the contacts themselves (oxidation)
Searching for a short circuit
One method for finding a short circuit is to remove the fuse and connect a probe lamp or voltmeter instead. There must be no voltage in the circuit
Pull the wiring while watching the probe lamp. If the lamp starts flashing, there is a short to ground somewhere in this wiring harness, possibly caused by chafing of the wire insulation
A similar test can be carried out for each of the components of the electrical circuit by turning on the appropriate switches.
Checking the reliability of contact with the "mass"
Disconnect the battery and connect to a point with known good contact with the "ground" one of the wires of the probe lamp, which has an autonomous power source
Connect the other lamp wire to the wire harness or connector pin you are testing. If the lamp lights up, contact with "ground" is in order (and vice versa).
An continuity test is performed to detect open circuits. After disconnecting power to the circuit, test it with a self-powered test lamp. Connect the probe leads to both ends of the circuit. If the test lamp lights up, there is no open in the circuit. If the lamp does not light up, then this indicates an open circuit in the circuit. Similarly, you can check the health of the switch by connecting a probe to its contacts. When the switch is turned to the "ON" position, the probe lamp should light up.
When diagnosing a section of an electrical circuit that is suspected of being open, visually detecting the cause of the malfunction turns out to be quite difficult, since it can be difficult to visually check the terminals for corrosion or a violation of the quality of their contacts due to limited access to them (usually the terminals are closed by the contact connector housing). A sharp twitch of the body of the wiring harness block on the sensor or the wiring harness itself in many cases leads to the restoration of contact
Keep this in mind when trying to isolate the cause of a circuit failure that is suspected to be open.
Intermittent failures may be due to oxidation of the terminals or a deterioration in the quality of the contacts.
Diagnosing faults in electrical circuits is not a difficult task, provided it is clear that the electric current is supplied to all consumers (lamp, electric motor, etc.) from the battery through wires through switches, relays, fuses, fuses, and then returns into the battery through the "mass" (body) of the car. Any problems associated with electrical equipment failure can be caused by the loss of electric current to them from the battery or the return of current to the battery.