Given the bulky nature of 12volt adapters for vehicles, I decided to integrate a USB power outlet in my 2010 Prius III. Although this mod is specific to my car, it can be applied to many cars, trucks, RV's, boats, ect.
Step 1: Finding a location for the USB power plug
In the 2010 Prius III there is an unused outlet next to the 12volt aux power in the front center console. I disassembled the center console and removed the plastic housing of the blank outlet and the 12volt aux.
Step 2: The USB 12 volt car adapter
I disassembled a Dynex USB power adapter and removed the circuit board from the plastic housing, then removed the 12 volt supply wires. The supply wires were springs and such, and too bulky to reuse.
Step 3: Preparing the blank cover
Once the blank cover (plug) is removed, I found it to be filled with a dense lattice of plastic. To fit the USB power circuit in it, a lot of the plastic needed to be cut out. Using an Exacto knife, and a box cutter, I cleared the inside of the cover.
Step 4: Fitting the USB circuit board
I used a Dremel tool with a grinding attachment to slim down the USB's circuit board until it slid into the hollowed out cover. Once the fit was right, it was time to make the hole on the face to access the USB plug.
Step 5: Making the hole for the USB power
I approximated the center of the USB plug and drilled a tiny hole through the face of the blank accessory plug.
Step 6: Wiring
Once I trimmed the opening, It was time to wire the 12 volt power to the USB adapter. Since the 12 volt accessory was right next to it, I soldered the ground from the USB board to the cigarette adapter, and attached the positive end to a nut on the back.
Step 7: Fixing the LED
The USB board has a 2 color LED to indicate power and charging. I wanted the light to shine behind the USB plug, so I de-soldered the LED and repositioned it to face forward. I had to add some wire to the board to attach the LED, but it was not hard, and could be done by a beginner.