The disconnect solenoids are usually (always?) the latching type so that no voltage/power is required except when switching. There are two signal terminals and reversing the polarity (swapping plus and minus) switches the solenoid from one state to the other. The solenoid may need to be replaced. I would put a voltmeter on the two terminals and watch while someone presses and holds the switch one way and then the other. If the voltage is there and reverses polarity but the solenoid does not activate then you probably need to replace it.