you can also use a relay switch between the DD5 header and fans. We are using 10A DPDT relay switch for auto 7V to 12V mod for DD5.
The relay switch also acts as an insulator between the DD5 header and fan (or fans). Check out PH's review of our AquaXtreme XG case. There's a section called "customized DD5" where he's giving more info about our relay switch mod.
Bruce
www.cooltechnica.com