I have a Gigabyte Triton case which has a front and rear fans. Front fan has its own connector which I plugged into MB's Sys_fan and works fine. The rear fan however doesnt work. It doesn't have its own connector it is joined to the front fan power cable, and it doesnt spin up. I was wondering if perhaps it might be wired up wrong or the motherboard pin can't power two fans off the same fan connector. MB is a Gigabyte 965P-DQ6, I think both fans need 12 V at 0.2 A. Perhaps I should make the rear fan its own cable and connect it to the unused pwr_fan connector on the motherboard. Any ideas?
I have no precise idea what voltage you are getting out of your mobo header, but perhaps it IS only 5V (not altogether likely), which means a 12V fan most likely wont power up. Hack into the yellow/black cable pair on a molex connector, put your extra fan on that. It wont be speed controlled by any temp regulation, just flat out at 12V.