Night Vision in Call of Duty 4 (Wii): Not Available

You cannot enable night vision in Call of Duty 4: Modern Warfare on Wii. The feature simply doesn't exist in this port.

Night vision appears in specific missions/weapons in later Call of Duty titles (e.g., MW2 thermal scopes, Black Ops NVGs), but the Wii version of CoD4—based on the PS2 codebase—omits it entirely.