The on-board electrical equipment includes a number of relays and control units, which are placed in a protective box on the left under the dashboard or under the steering column lining.
A simple switching relay is used for powerful current consumers. If the current flows in long bypass paths through the wires through the appropriate switches, then there is a loss of voltage. In addition, the contacts of the switches are subjected to a heavy load due to the high current. In relay switching, switches are only used for low switching currents, so that the consumer is not connected directly, but via its own relay.
If the switching signal does not come from a switch, but from an electronic control unit, the same law applies: sensitive electronic components cannot conduct high currents without damage.
Certain relays may perform additional functions. For example, the Intermittent Pulse Relay, the Wash/Wipe Interval Switch Relay controls the wiper interval and dry running after the windshield washes.
Control units have more or less extensive electronic circuits for switching certain functions, sometimes another relay is also installed. Examples include the central locking control unit and burglary warning systems.
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