hi,

i whant to put a second hdd in my xbox but i have a question about the switch for the power cable.

do i only need to put the switch between the the 5v and 12v line or do i have to switch all the lines?

There are a couple of tutorials on the main page covering this.

You only need to switch the power lines. For an even simpler circuit only one power line needs to be switched. Which one it is I cant remember.