Before you begin troubleshooting any electrical circuit, carefully study the relevant circuit diagram to get a clearer idea of its functional purpose. The troubleshooting circle is usually narrowed by gradually identifying and eliminating normally functioning elements of the same circuit. If several elements or circuits fail simultaneously, the most likely cause of the failure is a blown fuse or a broken ground (different circuits can often be shorted to the same fuse or ground terminal).
Electrical equipment failures are often due to simple causes such as corroded connector contacts, a blown fuse, a blown fuse link, or a damaged relay. Visually inspect all fuses, wiring, and connectors in a circuit before attempting a more detailed inspection of the components.
When using diagnostic tools to locate a fault, carefully plan (in accordance with the attached electrical diagrams) where in the circuit and in what sequence the tool should be connected to ensure the most effective fault detection.
The 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), a circuit breaker indicator (probe), which includes a lamp, its own power source 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 (another car's battery), equipped with crocodile clips and, preferably, an electrical circuit breaker. They can be used for bypassing and connecting various elements of electrical equipment when diagnosing a circuit. As already mentioned, before you start checking the circuit using diagnostic equipment, determine the connection points according to the diagrams.
Checking for the presence of supply voltage are carried out in case of a fault in the electrical circuit. Connect one of the leads of the electrical circuit tester to the negative terminal of the battery or ensure good contact with the car body. Connect the other lead of the tester to the contact of the connector of the circuit being tested, preferably the one 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 serviceability of the circuit between this point of the circuit and the battery. Proceed in the same way to examine the rest of the circuit. Detection of a supply voltage fault indicates the presence of a fault between this point of the circuit and the last of the previously tested (where there was supply voltage). In most cases, the cause of the failure is loosening of the contact connectors and damage to the contacts themselves (oxidation).
Searching for the location of a short circuit. One method of finding a short circuit is to remove the fuse and connect a test lamp or voltmeter instead. There should be no voltage in the circuit. Pull the wiring while watching the test lamp. If the lamp starts to blink, there is a short to ground somewhere in the wiring harness, possibly caused by chafing of the wire insulation. A similar check can be made for each component of the electrical circuit by turning on the appropriate switches.
Checking the reliability of the contact with the "ground". Disconnect the battery and connect one of the wires of the test lamp, which has an independent power source, to a point with a known good contact with the "ground". Connect the other wire of the lamp to the wiring harness or connector contact being tested. If the lamp lights up, the contact with the "ground" is OK (and vice versa).
Checking for breakage. The test is carried out to detect breaks in the electric circuit. After disconnecting the power supply to the circuit, test it using a test lamp with an independent power source. Connect the test leads to both ends of the circuit. If the test lamp lights up, there is no break in the circuit. If the lamp does not light up, this indicates that there is a break in the circuit. In a similar way, you can check the serviceability of the switch by connecting the test lamp to its contacts. When you move the switch to the "ON" position, the test lamp should light up.
Localization of the break point. When diagnosing a suspected open circuit section of an electrical circuit, it is quite difficult to visually detect the cause of the malfunction, since it can be difficult to visually check the terminals for corrosion or poor contact quality due to limited access to them (usually the terminals are covered by the housing of the contact connector). A sharp twitch of the housing of the wiring harness block on the sensor or the wiring harness itself in many cases leads to the restoration of contact. Do not forget about this when trying to localize the cause of failure of a suspected open circuit. Unstable failures can be a consequence of oxidation of the terminals or poor contact quality.
Diagnosing electrical circuit faults is not a difficult task, provided that you clearly understand that electric current flows to all consumers (lamp, electric motor, etc.) from the battery via wires through switches, relays, fuses, fuse links, and then returns to the battery through the "ground" (body) of the car. Any problems associated with the failure of electrical equipment can be caused by the cessation of the supply of electric current to them from the battery or the return of current to the battery.
(The original version can be found on the website: FORDBOOK)