Malfunctions in electrical circuits usually occur for relatively simple reasons, such as loose or corroded contacts, a blown fuse or a failed relay. Therefore, before starting to repair a failed circuit, make a visual check of the condition of all fuses, wires and contacts in this circuit.
If you are going to use measuring devices, plan in advance, based on the study of the circuits, where they should be connected in order to accurately find the fault.
The main instruments needed for troubleshooting electrical circuits are a tester or a voltmeter (you can also use a 12-volt test lamp with a set of wires).
Voltage test
If the circuit is not working properly, check the voltage in it. Connect one of the tester leads to the negative battery terminal or to "mass". With the second terminal of the tester, touch any electrical contact of the circuit under test (preferably closest to the battery) or to the fuse. If the tester lamp lights up, this means that there is voltage in the circuit and the section of the circuit between this electrical contact and the battery is working. Check the rest of the chain in the same way. When you reach a point where there is no voltage, it will mean that the fault is between that point and the last point where there was voltage. In most cases, the malfunction comes down to a loose contact.
Note. Note that some circuits are only energized when the ignition key is in the "Accessory" or "Run".
Short circuit detection
One method for detecting a short in the circuit is to remove the fuse and connect a test lamp or voltmeter to the terminals instead. In this case, there should be no voltage in the circuit. Move the wire harness from side to side while observing the test lamp. If the lamp lights up, it means there is a short circuit to the "mass" somewhere nearby, perhaps where the insulation has frayed. Any element of the circuit, including the switch, can be subjected to a similar test.
Checking contact with "weight"
Checking for contact with "weight" performed to ensure a good connection with "weight" any element of the circuit. After disconnecting the battery, connect one of the outputs of the test lamp with its own power source (this device is called a continuity tester) to a contact known to be connected to "weight". Connect the other end of the wire to the wire you want to test. If the lamp lights up, then the connection is good.
Continuity Test
A continuity test is performed to determine if there are breaks in a given circuit (if under normal conditions it passes current). Disconnecting the circuit (it shouldn't be stressed), you can use a continuity tester with its own power supply to check it. Connect the test leads of the tester to both ends of the circuit, and if the lamp lights up, then the circuit is conducting. If the lamp does not light up, then there is an open somewhere in this circuit. The circuit breaker can be tested in the same way by connecting a continuity tester to its contacts. When the switch is turned on, the lamp should light up.
Break detection (open circuit)
When checking electrical equipment to determine the possible presence of an open circuit, its visual detection is often difficult, since oxidized areas or loose contacts are hidden in electrical connectors. Sometimes it is enough to move the electrical connector on the sensor or the wiring harness to restore contact. This should be kept in mind when looking for open circuits. Intermittent open circuits can also be caused by oxidized or loose contacts.
Troubleshooting electrical equipment becomes relatively easy if you consider that the current in all electrical circuits goes mainly from the battery through wires through switches, relays and fuses to all electrical devices (lamps, electric motors, etc.) on "mass", from where it returns to the battery. Therefore, any malfunction in the electrical circuit is essentially nothing more than an interruption in the electrical current coming from the battery and returning to it.