The drive should have 2, maybe three connectors on the back edge. The optional one is a 4 pin power supply at the right hand side.......
EDIT: Scratch that, I'm talking bullpoop. Just checked a spare drive and I had the connectors round the wrong way. There should be a pair of L shaped connectors at the left hand side, the larger left hand one is the power connector (use this or the 4 pin molex but not both). Immediately to the right of the SATA power connection there should be a smaller, similar connector for the SATA data cable.