An emergency light bar mounting assembly for either trucks without a cargo box that extends vertically above the level of the cab, or for trucks having a bed that is lower than the cab, provides additional vertical clearance for the vehicle when needed, by having an emergency light bar mounting platform hinged to an immovable horizontal frame member. The mounting platform is rotated to a horizontal position when the light bar is in use, but rotated to a vertical position when greater vertical clearance is needed for the vehicle on which it is mounted. When the mounting platform is vertically positioned, the contribution of the emergency light bar to the height of the vehicle is completely eliminated. Rotational movement of the mounting platform is accomplished using an electric, hydraulic, pneumatic or manual drive system.