lol Gene. He probably posted in the wrong section to begin with and Harry had to move it to here.
There are a couple of ways to do a black wash on grilles, wheels, etc.
1) Thinning down Flat Black Acrylic with water like mentioned above. Once dry, you a Q-Tip or Cotton Ball to rub the black away from areas where its not needed. You can even dip the end of a Q-Tip in Alcohol for instant removal. DO NOT SOAK THE Q-TIP!! Alcohol will eat the plastic. If you use is scarcely, it will be fine. Doesn't take much trust me.
2) Depending on the size of the grill, I will sometimes spray it flat black and before it has a chance to fully dry, wipe away the areas you don't want covered using a Q-Tip or Cotton Ball.