It's the light green wire with a red easy splice on the end. If you want to be able to watch DVDs while in motion (for kids or passengers) cut the wire in half, install a basic $3 toggle switch to connect the two halves, and then run the easy splice to the black ground in the back of the head unit. Then simply turn your toggle switch on, off, and back on again and it fools the radio into thinking the parking break is on.
I have the same radio and love it!!
2005 F150 FX4 named "White Lightning"---black leather interior-factory upgraded audio-35% tinted windows-6" eyebrow-2.5" Hell Bent Steel leveling kit-high profile tool box-18x9 XD Monsters -12 offset, 295/70/18 Nitto Trail Grapplers-Flowmaster 40 series w/chrome tip