The screw holes are presumibly connected to ground, so the three wires from the motor are the phases. Links http://www.arvydas.co.uk/2012/07/fixing-a-seagate-7200-11-hard-drive-with-arduino/ http://atola.com/products/insight/manual/serial-port-connection.html http://www.malwaretech.com/2015/04/hard-disk-firmware-hacking-part-1.html https://sites.google.com/site/seagatefix/