Here the side trim is unscrewed (2) at the feet of the driver. The arrows show the mounting screws. Under it is a group of connectors (1).
Under the side cover (1) on the passenger side, next to the driver, there is also a group of connectors (2). The arrows show the mounting screws.
Central switching node (2) located in the Audi A4 on the left under the dashboard. Placed above «13-Position Auxiliary Relay Support» (1).
The figure shows the location of the jacks of the central switching node.
Standard terminal designations
The multi-colored mixing of wires in a car is actually very well ordered, as many parts of the car's electrical equipment are standardized. The numbers on different nodes and connecting elements of wires, as well as in electrical diagrams on all German and on some foreign cars have the same meaning:
Terminal 15 is only supplied with power when the ignition is switched on from the ignition switch, and in addition to the ignition/injection system, those electrical consumers are supplied with current, which should only receive current during vehicle operation. For wires to terminals 15, in most cases, the sheath is black, sometimes with a colored additional strip for certain current consumers.
Terminal 30 receives direct current from the battery positive or from the alternator when the engine is running. If the tools are handled carelessly, this can lead to short circuits or cause a rain of sparks if the wire connected to the battery minus is not removed. These wires, which are always energized, are in most cases red, sometimes with additional colored stripes.
Terminal 49 refers to the intermittent and emergency light system.
Terminal 53 supplies voltage to the windscreen cleaning system.
Terminal 56 supplies current to the low beam headlights on the yellow and yellow/black wires, and to the high beam headlights on the white and white/black wires.
Terminal 58 supplies power to the front parking lights as well as the rear lights and license plate light. The main color of the wire sheath is gray, sometimes with an additional color stripe.
Terminal 75 of the ignition switch is energized when the ignition key is in the «Included».
Terminal 31 – ground terminal, through which the electrical consumer must be connected to ground in order to close the electrical circuit. Corresponding wires have a brown sheath.
Labeled electrical connectors
In the Audi A4, the individual wires are often bundled in black sheathed bundles, making it difficult to find a particular wire. In this case, orientation assistance is provided by multi-pin connections, for which this chapter describes the exact number of wires and their exact location in electrical diagrams.
Wires
The cross-section of the wire is selected depending on the power supply needs of each consumer: the control light is supplied with a wire 0.5 mm thick2, and the starter needs a wire 16 mm thick2. Too thin wire heats up, and the voltage drops. Then, instead of the desired 12 V, for example, on the headlights, maybe only 10 or 9.5 V comes in - the light becomes dim.
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