During installation, only apply pressure at the tab ends on the underside section of the air horns, DO NOT install by exerting pressure on either of the tubular sections of the air horns – otherwise one or both of the horn tubes may break off. It is advisable to handle the air horns by the rectangular body section only. Locate the front and rear rectangular openings on top of the cab unit. Sometimes there can be plastic flashing in one or both of the openings that can be detrimental to air horn installation; and there can also be excess plastic in between the two rectangular openings of the cab unit. Clean any excess plastic off very carefully with an Xacto knife, so you have a pair of rectangular openings and a cab unit that look like the picture above. Install per the following two steps: 1) Insert the rear tab on the air horns into the rear rectangular opening on top of the cab unit; 2) Apply gentle pressure on the front tab on the air horns while inserting that tab into the front rectangular opening on top of the cab unit, and lock the front tab in place. Only apply gentle pressure to the air horn front tab during installation. DO NOT apply any pressure whatsoever onto the tubular portions of the air horns. Once the air horns are in place on the cab unit, leave them in there and do not remove.
Good Luck, and hope you enjoy the air horns.