Patent ID: 7557460

Claim:
An electric power source for a motor vehicle, comprising: a battery; a contactor shutting off a voltage outputted from the battery; and an interlock circuit controlling the contactor, the interlock circuit detecting a disconnected state of an interlock wire and turning off the contactor to shut off a power supplied from the battery, wherein the interlock circuit comprises: a current output circuit outputting a detectable current via a diode to the interlock wire; a first current detection subcircuit, connected via the interlock wire and the diode to the current output circuit, for detecting the detectable current outputted from the current output circuit; a second current detection subcircuit, connected to a connection point operatively located between the current output circuit and the diode, for detecting the detectable current outputted from the current output circuit; and a judgment circuit judging a disconnected state of the interlock wire, based on the detectable current detected at the first current detection subcircuit and the second current detection subcircuit, and thus cutting off the contactor, and wherein when the detectable current is detected at the second current detection subcircuit and when the detectable current is not detected at the first current detection subcircuit, the judgment circuit judges the interlock wire to be in a disconnected state and thus cuts off the contactor.