Headlight Ballast on 2003 Lincoln Navigator

How do you locate and replace the Xenon Head Light HID Ballast?on a 2003 Navigator

The headlight ballast is usualy on the bottom of the headlight assembly.Remove the assembly as if to replace the bulb/burner per the owners manual.
ok i have a question my front left factory hid turns on for like 2 seconds then turns off, someone told me it was the ballast its it costly to replace it and do u know of any shops in san antonio texas that can repair it or is it something i can do on my own