Computer Power Supply and Switch Wiring Questions

[rawfuls]

Wired up a temporary molex connector for 5V instead of 12V, the LEDs are dim, the fan doesn't spin, turn it about 100%, then to 25% (to get the fan started), and it'll spin, however there's no noticeable airflow until around the 75% mark... (You can say it BrianG... you told me so! ).

Looks like I'll be switching between 7V and 12V... maybe.

So, in order to wire up the "temporary molex" thing, I would have the negative black wire from the fan to the red wire (5V), and the positive to the yellow wire (12V), right?
And this will just push out a constant 7V?