POWER SOURCE PLUG FOR ON-VEHICLE EQUIPMENT

PURPOSE:To hold data of equipment and enhance, general purpose applicability by housing in a plug case a switching circuit for switching power supply between an auxiliary storage battery and an on-vehicle storage battery. CONSTITUTION:A power source plug for on-vehicle equipment is attached to or detached from a socket 2 having terminals on positive and negative electrodes of an on-vehicle storage battery 1. A positive terminal 3a is arranged at the tip of a plug case and a negative terminal 3b capable of elastically deforming in the diameter direction is arranged in the middle of a side wall, and an auxiliary storage battery 6 is housed so that its axial center is conformed with that of the case. A circuit 7 for switching power supply from the battery 1 to on- vehicle equipment 9 and power supply from the battery 6 is housed. The circuit 7 has a relay circuit 4 for switching power supply between first passages PI, P3 which supply power from the battery 1 to the equipment 9 and second passages P2, P3 which supply power from the battery 6 to the equipment 9. When power supply from the battery 1 fails, power is supplied from the battery 6.