Contents: Checking voltage ⤓ Short circuit detection ⤓ Checking the reliability of grounding ⤓ Checking the integrity of the circuit ⤓ Finding an open circuit ⤓
A typical electrical circuit consists of an electrical component, switches, relays, motors, fuses, fuse links or circuit breakers, and the wires and connections that connect all the components together and to the battery and (ground) of the vehicle. To make troubleshooting easier, electrical diagrams of the vehicle's electrical system are provided at the end of this chapter.
Before you begin testing a faulty circuit, first study the circuit diagram to understand what components it consists of. You can find the source of the fault faster if you determine which components of the circuit are working properly. If several components or circuits fail at once, the problem is likely a blown fuse or poor grounding, since one fuse often controls several circuits.
Problems with the electrical system are usually caused by simple causes, such as oxidized or unreliable contacts, a blown fuse, a burnt-out jumper, or a faulty relay. Visually check the condition of all fuses, wires (if possible), and connections in the faulty circuit before checking other elements of the circuit. If you are going to use instrumentation, use the circuit diagrams to determine which connections need to be checked to detect a fault.
The basic equipment needed to troubleshoot an electrical circuit is a voltmeter (or 12-volt light bulb with connecting leads), a continuity tester, a battery with connecting leads, and a jumper cable, preferably with a circuit breaker that can be used to connect in parallel to the circuit. Before you begin troubleshooting with test equipment, study the circuit diagrams to determine the connection points.
Checking voltage
A voltage test is necessary if the electrical circuit is faulty. Connect one of the test light probes to the negative terminal of the battery or (ground) of the vehicle. Connect the other probe to a connection in the circuit being tested, preferably as close to the battery or fuse as possible. If the test light comes on, voltage is present: this means that the part of the circuit between the connection and the battery is good. Continue checking the rest of the circuit in the same way. When you find a point where voltage is absent, this means that the source of the fault lies between this point and the last point where voltage was present. Most problems are caused by a poor connection. Note: Remember that in some circuits voltage is only present when the key in the ignition is turned to a certain position
Short circuit detection
One method of finding the short is to remove the fuse and connect a test light or voltmeter to the fuse terminals when all other electrical equipment in the circuit is off. There should be no voltage in the circuit. Move the wires from side to side and watch the test light. If it lights, one of the wires is shorting somewhere in that area, probably where the insulation has worn through. The same test can be done on any other component in the circuit, including the switch.
Checking the reliability of grounding
Perform a ground integrity test to check that the electrical component is securely connected to the vehicle ground. Disconnect the battery and connect one of the continuity tester leads to the vehicle ground. Connect the other lead to the ground connection or point to be tested. If the test light comes on, the ground is OK.
Checking the integrity of the circuit
A continuity test is necessary to determine if there is an open circuit. Disconnect power from the circuit and test the circuit for continuity using a light bulb with a power source connected. Connect the light bulb wires to the ends of the circuit (or to the positive end and "ground" of the car); if the test light comes on, there is no break in the circuit. If the light does not come on, there is a break somewhere in the circuit. You can also check the switch by connecting the test light to the switch terminals. After turning on the switch, the test light should come on.
Finding an open circuit
Visually finding an open circuit can be quite difficult, since oxidized or poor contact connections are often difficult to notice. Sometimes it is enough to simply move the connecting wire or wire in the wiring harness in order to eliminate this malfunction. Unreliable operation of electrical equipment components is also often caused by oxidized or poor connections.
Finding a fault in the electrical system seems to be a fairly simple operation if you understand that the electrical system operates based on the current flowing from the battery through wires, switches, relays, fuses and fuse jumpers to the electrical components (bulb, engine, etc.) and to the vehicle (ground), from where it flows back to the battery. Any fault in the electrical system is an interference in the current flow from or to the battery.