Making a molex to 3 pin fan cable.

I need a cable that will allow my power supply to power a couple of my CoolerMaster 120mm case fans. Since I don't feel like spending $5 a piece or waiting for shipping, I thought I might try to make them my self from the cables from an old power supply I have. I already have a male to 2 female molex adapter, so I need to make 2 male molex to male 3 pin fan cables. On the cables I make, I think I would only need to wire the 5 volt red and black wires from the molex to the fan connector, but I'm not sure. Do I need the 12v yellow wire for anything?