Recommendation. When searching for the causes of a malfunction of any electrical equipment, first make sure that its fuse is in good condition and that the contacts in its circuit are secure. A common cause of electrical equipment failure is oxidation of the terminals of the connection blocks, in which case they must be thoroughly cleaned. Pay special attention to the connection points of the negative terminals of the electrical equipment with the vehicle ground. Quite often it is the lack of reliable contact with the ground that leads to malfunctions in electrical equipment.
To troubleshoot electrical equipment, you should use a multimeter. If it is necessary to determine only the presence or absence of voltage on a section of the circuit, without measuring the value, it is more convenient to use a special 12 V light indicator...
...or a control lamp that you can make yourself (from a car lamp with a power of no more than 4 W, soldering two wires at least 50 cm long to it).
Note: The procedure for checking the technical condition of the vehicle's electrical devices is described in the relevant sections.
Very often the reason for the failure of electrical appliances is the oxidation of contacts in the wiring harness blocks. To eliminate the malfunction, it is enough to clean the terminals of the pads and treat them with a special conductive grease.
If any lighting fixture does not work (for example, a headlight, a turn signal, a light for the interior, etc), first, you should check whether the lamp has burned out, and only then check the electrical circuits.
The algorithm for checking electrical circuits is common for all electrical appliances. First, we check the fuse and relay of the inoperative device, which are usually installed on the fuse and relay boxes. We replace the blown fuse. If, when you turn on an electrical appliance, the fuse protecting its electrical circuit burns out again, there is a short circuit in the electrical wiring that must be urgently eliminated.
Warning! If you are not confident in your abilities, then contact a service station to repair electrical equipment, since unqualified repairs can lead to serious damage or fire in the vehicle's electrical wiring.
Further troubleshooting comes down to ringing the electrical circuits, which can be seen on the electrical equipment diagrams, and searching for faulty elements (wires, switch, device) and their replacement or repair.
(The original text can be found on the website «ChevyMan»)