NOVELTY - The device (10) has an electric current detection circuit (18) for detecting forward current that flows into a motor vehicle electrical component (28) and reverse direction electric current that flows into a battery (24) and outputting a detection signal. A logic circuit (20) carries out off control of a switch part (32) when the detection signal of the reverse direction electric current from the electric current detection circuit is received and carries out on control of the switch part when a detection signal of the forward current from the detection circuit is received.    USE - Power supply device for a motor vehicle electrical component e.g. power window, door lock, automobile accident automatic report system and illumination/lighting display apparatus (all claimed) such as hazard lamp and headlight.    ADVANTAGE - The device receives the detection signal of the forward current from the electric current detection circuit when the forward current flows into a motor vehicle electrical component side such that a logic circuit carries out on control of the switch part, so that the forward current flows into the motor vehicle electrical component side through a bypass line without going through via a diode when the forward current flows, thus preventing energy loss resulting from going through via the diode. The device operates an illumination/ lighting display apparatus even if output of the battery is stopped in an automobile accident, so that another driver is alerted to dangerous accident condition such as accident in nighttime highway, thus preventing induction of secondary accident. The device operates a power window and a door lock even if the motor vehicle encounters situations such as water immersion and submergence, thus securing passenger safety.    DETAILED DESCRIPTION - The switch part is a p-channel MOSFET. An INDEPENDENT CLAIM is also included for a motor vehicle electrical component unit.    DESCRIPTION OF DRAWING(S) - The drawing shows a circuit block diagram of a power supply device for motor vehicle electrical components.'(Drawing includes non-English language text)'    Power supply device (10)    Electric current detection circuit (18)    Logic circuit (20)    Battery (24)    Motor vehicle electrical component (28)    Switch part (32)