General description (Audi 80 B4)

When checking electrical equipment, a motorist, referring to technical documentation, constantly encounters such concepts as voltage, current, resistance.

Voltage is measured in Volts (IN), current strength - in Amperes (A), and the resistance is in ohms (Ohm) (see illustration 1.0).



When performing checks and repairs on the on-board electrical system and electronics, various measurements must be taken. To perform the desired measurement, you need an appropriate measuring instrument that ensures the accuracy of the measurements.

To perform many types of tests, a tester with a conventional incandescent bulb is very convenient. The connecting leads of the tester have so-called needle tips, which can be used to pierce the insulation of the wire under test. A tester with a test light first of all helps to find out if there is voltage on the tested node or component. By the degree of incandescence of the light bulb, one can judge the voltage in the circuit.


As for the details of electronic components, it is impossible to check the presence of voltage using a tester with a conventional incandescent bulb. The part being tested can be damaged. To check in such cases, a tester with a control diode bulb is used.

More accurate data can be obtained by measuring voltage using a voltmeter with a pointer or digital display. Due to the fact that the voltmeter consumes a small amount of current, it can be used for measurements on electronic components (see illustration 1.0a).



High voltages and high temperatures are dangerous for electronic components. Therefore, when working on the on-board network, certain precautions must be observed.

• A) Turn off the ignition before disconnecting the power plug of the electronic device, and best of all, disconnect the battery.
• b) Disconnect the battery and plugs of the relevant electronic devices when performing welding work on the body.
• V) Do not expose the vehicle to prolonged exposure to high temperatures. When placing the car after paintwork in the drying chamber, its temperature should not exceed 95°C. If the car is to be kept in the drying chamber for about two hours, the temperature in the chamber must not exceed 85°C.
• G) Start the engine only after the body (e.g. after drying chamber) cool down to ambient temperature.

The interlacing of wires in a car only at first glance seems chaotic. Many connections are standardized, and many part and terminal numbers are generally accepted


Terminal 15 is only powered by the ignition switch when the ignition is on. At the same time, in addition to the ignition coil, power is supplied to those consumers of the on-board network that should receive it when the car is moving. The wires on terminal 15 are insulated in black and only sometimes with additional colored stripes.

Terminal 30 is powered continuously from the positive battery terminal or from the alternator when the engine is running. This must be taken into account in order to avoid a short circuit when carrying out repairs without disconnecting the wire terminal «masses» (-) from the battery. This wire is usually insulated in red, sometimes with additional coloring.

Terminal 49 is connected to the turn signal and alarm breaker.

Terminal 53 supplies power to the wiper motor.

Terminal 56 supplies power to the dipped beam bulbs (wires have yellow and yellow-black insulation), as well as high beam. These wires have white or white-black insulation.

Terminal 58 powers the parking lamps, as well as the rear position and license plate lamps. The main color of the insulation of these wires is gray, sometimes with additional colored stripes.

Terminal 31 is the terminal «masses» (-), through which each consumer of electricity is connected to the car body. The corresponding wire has a brown insulation.

Individual wires are usually combined into bundles, which in turn are in a black sheath. This makes it difficult to find a specific wire. In this case, it is recommended to navigate using multi-pin connectors. Their location and the number of wires connected to them are indicated on the corresponding electrical diagram.

The cross section of the supply cable depends on the needs of the respective consumer. A 0.5 mm thick wire² is enough for a control light. The starter requires a 16 mm² power cable. If you install a wire of a smaller diameter than necessary, then such a wire will heat up, and the voltage in the circuit will decrease.

The connecting plugs are mechanically fixed to prevent their spontaneous disconnection. These clamps can be of different types. For example, the plugs of the injection system of gasoline engines and the power system of diesel engines have wire clips that must be pressed out to disconnect the plug. Most plugs have locking tabs on the housing that must be squeezed when disconnecting the plugs.