Checking the presence of supply voltage
Checks for the presence of supply voltage are made in the event of a malfunction of the electrical circuit. Connect one of the circuit tester leads to either the negative battery terminal or a well grounded point on the vehicle body. Connect the other tester lead to the electrical connector terminal of the circuit under test, preferably the one closest to the battery or fuse. If the tester's control lamp lights up, the supply voltage is present on this section of the circuit, which confirms the health of the circuit between this point in the circuit and the battery. Continuing in the same way, explore the rest of the chain. Detection of the absence of supply voltage indicates the presence of a malfunction between this point in the circuit and the last one previously checked (where the supply voltage was present). In most cases, the cause of the failure is the loosening of the electrical connectors and the deterioration of the quality of 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 starts flashing, there is a short to ground somewhere in the wiring harness, possibly caused by worn wire insulation. A similar check can be made for each of the components of the electrical circuit by turning on the appropriate switches.
Grounding check
This check is made to determine the reliability of the grounding of the circuit elements. Disconnect the battery and connect one of the wires of the self-powered probe lamp to a known well-grounded point. Connect the other lamp wire to the wiring harness to be tested or the electrical connector terminal. If the lamp lights up, ground is OK (and vice versa).
Check for continuity
The test is carried out in order to detect breaks in the electrical circuit. After turning off the power to the circuit, check it with a probe lamp equipped with an independent power source. Connect the probe wires to both ends of the circuit, if the test lamp lights up, there is no open circuit. If the lamp does not light up, then this indicates an open circuit in the circuit. Similarly, check the health of the switch by connecting a probe to its terminals. When the switch is turned to position «On» the probe lamp should light up.
Break location
When diagnosing an electrical circuit, it is quite difficult to find the cause of a malfunction in it, since it is difficult to inspect the terminals for corrosion or a violation of the quality of their contacts due to limited access to them (usually the terminals are covered by the body of the electrical connector). A sharp twitch of the connector housing on the sensor or the wiring harness in many cases leads to the restoration of contact. Intermittent failures can be caused by terminal oxidation or poor contact quality.