What's your car? Do you have the Ford "Premium" Audio system?
If so, you'll need an amp bypass kit, available from Crutchfield.
Otherwise, you'll need a wiring diagram for the stock Ford wiring harness (there are a few on this site... just search around), as well as a diagram for the JVC head unit.
As far as the physical install goes-
http://members.fortunecity.com/bk4293/contour/stereo.htmlThat's the Crutchfield Master Sheet for the Contours.
Enjoy!