Pioneer D3 "night Mode/dim"

[reddedsilvy05]

ok i have a 05 silverado with a Pioneer D3 in dash head unit.... I want to hook up the illumination wire so the screen will dim at night when the lights are on but it does not work with the GMOS "Ilummination" wire....apparently you have to wire it to the dimmer wire on the light switch harness...im having a problem locating that wire because i do not know what color it is....if anyone knows please let me know....thanks guys