Abstract: A multivoltage vehicle electrical system for supplying electrically operated loads in motor vehicles, specific loads being respectively assigned to each vehicle electrical circuit which is respectively operated with a different voltage, is characterized in that cross-connecting means are provided which, in the event of a failure or fault in a circuit, automatically ensure that the loads connected to this failed vehicle electrical circuit are supplied from one of the other vehicle electrical circuits.

Abstract: A motor vehicle electrical system has an electrical machine with an on-board power supply generator function. The electrical machine can be operated, in a first mode, as an on-board power supply generator, having a regulator for setting the excitation current for the electrical machine, and having an electrical load having a comparatively high power consumption, for example a heating device for an exhaust gas catalytic converter. A changeover switch, by means of which an output of the electrical machine can optionally be connected to an on-board power supply cable or to the load, as well as a control unit for controlling the regulator and changeover switch optionally in the first mode or a second mode, is provided so that the electrical machine is connected to the on-board power supply and the regulator regulates the operating voltage at an on-board power supply voltage. Alternatively, the electrical machine is connected to the load and the regulator regulates the operating voltage at a higher nominal value.