Abstract: An electrical heating arrangement for a motor vehicle comprises a heating resistor that is energizable directly by the power generator provided that within a network of consuming devices failure has been detected and also provided that essential elements of the network such as battery or engine temperature are within predetermined limits. Upon detection of a failure this error condition is optically indicated and the connection between the heating resistor and the generator is interrupted.

Abstract: The electrical system of a motor vehicle is protected against damage due to voltage sources, either the own battery or an external source, connected with wrong polarity by the combination of a diode and relay switches. In one embodiment, the diode is connected to the battery so that current flows only when the battery is connected with the correct polarity. The relay coil connected in series with the diode controls contacts which connect the battery to the rest of the circuit only when current flows through the diode. Alternatively, or in conjunction with this type of circuit, a shunting diode can be provided through which current flows only when the battery is connected with incorrect polarity. When current flows through this shunting diode, it also flows through the contacts of excess current cutout which then open to disconnect the battery from the remainder of the circuit.