How to change spark plugs on a GT mustang are the same from 1999 to 2004 Mustang V8 4.6L
They are located on top of the engine. You first have to remove the coil packs, which there are 8 of them, one goes over each spark plug. They are located side by side of your fuel injectors. If you locate a fuel injector and wiring plug, right next to it is a coil pack with a plug. Unplug the the wiring plug that is located at the tip of the coil pack, unscrew the tiny screw located on the right side of each coil pack, pull the coil pack up and out (They also have rubber boots located at the bottom of the coil pack) and the spark plug will be located under it (No different than if you had spark plug wires and you pull the boot off to access the spark plug) Hope this helps!