Rather than re-create the entire fog light circuit, it is possible to just replace the factory relay with one of your own and use 100% factory wiring!
First, Read this thread for reference, there is a lot of good information in here and plenty of helpful pics:
Original Fog Light Mod
(Great work DipStick)
Then take a look at the attached .pdf's. They are pages from the Service Manual that describe the fog light circuit and function.
Now for the cool part...