It plugs into the motherbd's front panel header section. Consult your motherbds owners manual for which set of pins is the hdd_led. The from panel connector is usually labelled right on the connector. If the connector is properly connected and your drive is not using an add in card (like a raid card) then unplug the connector and spin it around 180 and plug it back in. and try again. If that doesn't fix it, then the wiring or led is faulty.