Abstract: An interface circuit for effecting switchover between plural hot melt material delivery systems so that hot melt material can be continuously supplied to applicators or the like. There are two similar relay circuits which are interconnected so that upon depletion of hot melt material from one system, operation is automatically transferred to another system. The relay circuits each include disconnect contacts for disconnecting the depleted system, transfer contacts for activating the new system, lock-out contacts for preventing operation of the system that is not activated and lock-in contacts for activating the new system without attention by the system operator. The coil of the disconnect relay can be connected to a delay circuit so that deactivation of the depleted system can be delayed by delay interval after activation of the new system. The delay circuit affords a fixed delay interval or a variable delay interval.