Abstract: A combination of a magnetically-actuated interlock switch assembly and an actuating magnet unit, and a method for their use, in which a supply current is connected to ground potential so as to overload and open a fuse in a power supply input line when the interlock fails to open in response to absence of the actuating magnet within a required proximity to the interlock switch assembly. A more sensitive magnetic reed contact opens upon approach of the actuating magnet, before a less sensitive magnetic reed contact closes in response to closer approach of the actuating magnet to provide a biasing control voltage to a transistor which is thereby turned on to provide power to the load. Should the transistor or the switch providing the biasing voltage to the base of the transistor remain in a conductive state when the actuating magnet is removed from proximity with the switch assembly supply power is short-circuited, opening the fuse. Provision may be made for an interlock status indicator.