In this post you'll find a basic HID write-up. The HIDs I bought came with a wiring diagram. You will not find an extensive "how-to" in this post, merely the mounting points that I used in conjunction with the wiring diagram.
This is where I mounted and grounded the resistor for the left HID.
This is where I mounted the ballast on the left.
This is the ground point I used for the wiring harness NEEDED for the Focus in order to prevent the "low-beam bulb out" error.
Same thing on the right side for the resistor and ground point.
Same location for the ballast as the left.
The black covered wires (the one with writing on it) is the HID wiring. It is what connects the left to the right. I wired it along the front of the car and zip-tied. There is enough wire for slack at either end if routed and done properly. The red wire, you'll notice, is the positive wire for the DRLs.
This is the ground point for the right Focus specific wiring harness.