I thought that the pin layout was a such with voltages:
red-black-black-yell with the red/black combination being your 5V supply and the yellow/black being the 12V supply.
To make things easier, here is my suggestion. Instead of splicing any wires on the computers power supply, I would look at the following website.
http://www.coolerguys.com/840556052166.htmlThey have a nice PCI Molex connector. I belive all these connectors will be using the 5V and 12V supply from the PS. I would disconnect the red/black cable if there is any on the GGG hardware. If not great, just plug the device into the molex connector and your 12V will be supplied. That is if the 12V is already tied into the appropriate male/femal molex connector. It would be easy enough to splice into a molex connector by obtaining a molex Y splitter and or a molex extender.
Hope this helps out. Thanks, Shane