Intro: HOW TO FIND OUT WHICH WIRE HAS POWER IN a USB CABLE
I checked it out @ Techshop
Quick answer: RED and BLACK
Step 1: First, You Will Need to Find an Used USB Cable, a Multimeter and a X-acto Blade.
(You can't see but the red and black wires are already peeled, may be someone tried before me to extract power from this cable)
Step 2: Then You Need to Peel the Wires
Step 3: Connect Your USB Cable to a Computer
Step 4: With the Multimeter Start to Hunt for Which Pair of Wires Measures Around 5V.
Step 5: It Is ... the BLACK and RED Pair
Step 6: Now Go Find a USB Female Port
Step 7: Cannibalize the Circuit
Step 8: Take Out the Plug
Fit the female plug into your power source
(the USB cable has 4 wires, and in this case the 2 outside wires were the power ones)