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 the failure is the blown out of the corresponding fuse or a violation of contact with «weight» (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 damaged 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.
If using diagnostic tools for troubleshooting, carefully plan (in accordance with the attached wiring diagrams), at which points of the circuit and in what sequence the device should be connected for the most effective fault detection.
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), open circuit indicator (probe), including a lamp, its own power supply and a set of connecting wires. In addition, you should always have a set of wires in the car for starting the engine from an external source (battery of another car), equipped with clip type «crocodile» 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 to check the circuit using diagnostic equipment, determine the connection points from the diagrams.
Checking the presence of supply voltage carried out in the event of a power 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. Proceed in the same way, explore the rest of the chain. Detection of a power failure indicates the presence of a malfunction between this point in the circuit and the last one previously checked (where was the supply voltage). 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 should be no voltage in the circuit. Pull the wiring while watching the probe lamp. If the lamp flashes, there is a short to voltage somewhere in this wiring harness «mass», possibly caused by chafing of 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 «weight». Disconnect the battery and connect to a point known to be in good contact with «weight» 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 «weight» in order (and vice versa).
Check for continuity carried out to detect breaks in the electrical circuit. 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 position «ON» the probe lamp should light up.
Break location. 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 (normally the terminals are covered by the 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.
Diagnosis of 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 to the battery through «mass» (body) 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.
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