Attention! Read the safety precautions (see section 14) before starting work.
Warning: The following tests are intended to check basic electrical circuits and should not be used to check sensitive electrical circuits (such as the ABS system), especially if there is an electronic control unit in the circuit.
A typical electrical circuit consists of a piece of electrical equipment, switches, relays, motors, fuses, fuse links or circuit breakers, and the wires and connections that connect all the components together and connect them to the battery and (ground) of the vehicle. To simplify the troubleshooting process, in subsection 14.20 the electrical diagrams of the vehicle's electrical system are provided.
Before you start checking a faulty circuit, first study the circuit diagram to understand what elements it consists of.
The source of the fault can be found more quickly if you determine which elements of the circuit are working properly.
If multiple components or circuits fail at once, the problem is likely a blown fuse or poor grounding, as often a single fuse controls multiple circuits.
Electrical system problems are usually caused by simple issues such as corroded or loose contacts, a blown fuse, a blown fuse link, or a faulty relay (see the relay test procedure in subsection 14.3).
Visually inspect the condition of all fuses, wires and connections in the faulty circuit before testing other components of the circuit.
If you are going to use test equipment, use the schematic diagrams to determine which connections need to be tested to locate the fault.
The main devices needed to find a fault in an electrical circuit are a voltmeter (or a 12 volt light bulb with connecting wires), circuit integrity testing device, ohmmeter (for measuring resistance), a battery with connecting wires and a jumper cable, preferably with a circuit breaker that can be used for parallel connection to the circuit.
Before you begin troubleshooting using test equipment, study the circuit diagrams to determine the connection points.
To find a loose connection or short circuit point (usually due to a poor or dirty connection, or damaged insulation) the wires can be shaken by hand to see if the circuit breaks when the wire is moved. In this way, a point with a poor connection or a point where a short circuit occurs can be found. This method of testing can be used along with the other tests described in the following subsections.
Besides problems associated with a poor connection, an electrical circuit can have two other main faults - an open circuit or a short circuit.
An open circuit can be caused by a broken wire or a loose connection somewhere in the circuit that prevents current from flowing. An open circuit will cause a piece of electrical equipment to fail to operate, but will not cause the fuse for that circuit to blow.
Short circuit faults are caused by a short somewhere in the circuit, causing the current flowing in the circuit to flow into another circuit, most often to (ground). A short circuit is usually caused by a break in the insulation, allowing the supply wire to touch either another wire or a grounded element, such as the body. The short circuit causes the fuse for the corresponding circuit to blow.
Breaking the chain
To find an open circuit, connect one of the test light probes to the negative terminal of the battery or (ground) of the vehicle.
Connect the second probe to a connection in the circuit being tested, preferably located as close to the battery or fuse as possible.
Apply voltage to the circuit. Remember that some circuits only have voltage when the ignition key is turned to a certain position.
If voltage is present (what will the illuminated control lamp or voltmeter readings indicate?), this means that the part of the circuit between the connection and the battery is OK.
Continue checking the rest of the chain in the same manner.
When you find a point where there is no voltage, it means that the source of the problem lies between this point and the last point where voltage was present. Most problems are caused by a bad connection.
Short circuit
To test a circuit for a short circuit, first disconnect the circuit's load (loads are the electrical components that consume electricity, such as light bulbs, motors, heating elements, etc.).
Remove the fuse for the appropriate circuit and connect a test light or voltmeter to the fuse connection terminals.
Apply voltage to the circuit. Remember that some circuits only have voltage when the ignition key is turned to a certain position.
If voltage is present (what will the illuminated control lamp or voltmeter readings indicate?), this means that there is a short circuit in the circuit.
If there is no voltage, but the fuse still blows when connecting the load elements, then one of these elements is faulty.
Checking the reliability of grounding
The negative terminal of the battery is connected to (ground) most electrical equipment systems are designed so that only one supply wire is connected to the electrical element, and current is returned through the metal of the car body.
This means that the electrical component mount and the vehicle body are part of the electrical circuit.
Therefore, poor or oxidized fastening can cause a large number of problems in the electrical system, from complete failure of the circuit to its unreliable operation.
In particular, light bulbs may burn dimly (especially if another circuit is connected that uses the same ground), engines (for example, windshield wiper motors or radiator cooling fan) may operate slowly and turning on one circuit may affect the operation of another circuit.
Note that many vehicles use grounding straps between various components of the vehicle, such as between the engine/gearbox and the body, usually where there is no metal to metal contact between the components due to the use of rubber mounts etc.
1. Disconnect the battery and connect one of the ohmmeter probes to the vehicle ground.
2. Connect the second probe to the wire or ground point you want to test. The resistance registered by the ohmmeter should be zero; if not, check the connection as follows.
3. If you think the connection is not OK, disassemble the connection and clean the contact surface and the wire terminal or the surface of the grounded element down to bare metal.
4. Remove all dirt and corrosion, then use a knife to remove the paint layer to create a secure metal-to-metal bond.
5. When assembling, securely fix the connection; when installing the wire terminal, use toothed washers between the terminal and the body.
6. After connecting, to prevent corrosion, apply a layer of Vaseline or silicone grease to the connection, or treat it with a sealant such as (Holts Damp Start) or a water-repellent lubricant such as (Holts Wet Start).