sorry for the late response-
if there is power present on the orange wire, the lights in your radio will dim automatically.
If there is no power present on the orange wire, your radio lights will be at their brightest, assuming that you have your radios backlight set to "Auto"(menu-->settings-->set backlight-->Auto)
The theory is that while in your car, the backlight is brightest during the daytime so that you may see the display better. When you turn on the lights in your car, It dims the radios backlight during nighttime driving so as not to blind the driver from "too bright" a backlight while driving at night.
If the orange wire shares the same power as the red wire, and the radio backlight is set to auto, then your backlight will always be on a dim setting.
If you dont care to have it dim at all, you can just cap off the orange wire and omit its connection altoghether.