I am currently working on a project in which two small computer fans are powered from a USB port. I want to be able to get two laptop fans powered off of one USB slot.
I was looking into some solutions, and I found a power cord that matches exactly what I want to do. The thing I am confused is that when the power cable is split, the cables 
double at the point it splits, which is also the point in which I want to solder to the USB wire.
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The problem I face is that the USB only has 4 single free cables , not two cables on top of each other in each pin slot like where the Y split Molex cable above, so I can confused as to how I would attach it to the USB if there is one more cable on all slots? Are the cables attached at the end by one of those Molex pins, and then I just solder the pins to the exposed USB wire?
Furthermore, there are two black wires in seperate pins on the Split Molex cable, which one would I solder to the USB, as I know the only red cable would be soldered to the only red cable on the usb.
In comments: How would I solder the Molex connector to a USB if the molex connector has 2 wires seperated into 4 sections (as the USB cable only has one wire separated into 4 sections). If you look at my last picture, would I just solder those metal pins directly to the exposed wire on the usb, or would I chop those pins off, solder the two wires on the molex together, then solder the now combined wires to the usb wire?
Best Answer
On such a Molex connector, yellow is for +12VDC and red for +5VDC. Both black wires are ground (GND) or 0V, the return path. Either of the black wires will do... although, by convention, you might want to use the black wire that is close to the coloured cable for the power signal return path.
The yellow wire is useless for you since USB only has +5V on its (typically) red wire. you can then keep only the red wire and one of the black ones. Be sure to pair the wires that you keep with the fan's on the other connector.
You can safely chop the data wires (+ and -) off the USB cable. Better insulate them to prevent accidental shorting or contact with the power wires.