i took the grille out of the shell, cleaned it good. and sprayed it. no adhesion promoter or nothing, but i'd suggest it. I painted it a good 3+ years ago and it's still black and could use another shoot here sometime.
I'm trying to find my damn pic that i had with the grille.
EDIT: (found lil bro's trucks pics but not mine. lol)
after(fusion satin black):