Do the molex connectors provide 12v or 5v? I'm confused. Some stuff has the full set of wires, whilst others (blowers and fans) only get red and black. Jeez I must sound like a real dumbass...
Molex connections from your power supply provide 5v and 12v. The yellow wire is a 12v lead, the red wire is a 5v lead and the two black wires in the middle are ground lines. Some fan makers tend to just use red and black wires for the connections to 12v and ground respectively, but just see where it hooks into the molex and you will know which rail it is drawing from.
this is something i've always wondered about: if i have a switch which changes the feed to a fan from 12v to 5v does it matter which ground i use...i mean does the ground next to the 12v have to take the live from the 12v? or does it not matter?
technically they have two grounds because you need two sets of wires.... if they had only one ground it could lead to problems with voltages.... generally, its better to use the ground next to the +V line you're using
There are many reasons for having two ground lines. The 4-pin molex is typically used for HDD and CD/DVD drives. In these devices you will use both 5V (for the logic) and 12V (for the motor(s)). The motors will have back-EMFs and generate a lot of noise, which all goes onto the ground for the 12V line. Thus, the noise does not affect the more sensitive logic, which is grounded on the ground for the 5V. Also, a single ground line for both might have to carry a large amount of current, whereas two separate lines split the current.
