To pinpoint the exact location, you'll need a repair manual specific to your 2004 Ford Explorer V8 with the automatic transmission. These manuals usually have detailed diagrams showing the location of all the components of the transmission and valve body. A picture search online showing a 2004 Explorer V8 transmission valve body might also help you visually identify it once you've accessed the transmission. Be aware that accessing the valve body requires specialized knowledge and tools; this isn't a beginner-level repair.