I checked the OSPi 1.2 board, and here is the deal: the 24V pin you see is connected directly to one of the transformer pins, and it’s not even through the switch, so as soon as you plug in the transformer you should get 24V AC between the 24V pin and the GND pin. If not, you should definitely check if your multimeter is turned to AC voltage — if you measure DC voltage, you will get almost 0.