In 1968, the four-door hardtop was discontinued, leaving three models—the 500 and Monza Hardtop Coupes and the Monza Convertible. Air conditioning was dropped as an option, due to concerns about thermal loading added by the now-standard Air Injection Reactor ("smog pump") which probably hurt sales as factory air became more popular generally in automobiles. The GM multiplex stereo system was also discontinued when new units changed wiring adapters; the Corvair's 9-pin connector would no longer fit the new units. Additional safety features, including side marker lights, and shoulder belts for closed models, were fitted per the federal government's requirements. Steering wheel for 500s was the same as the base Nova's, while Monzas got the same wheel as the Camaro. An Impala-style "Deluxe" steering wheel was optional. All advertising was virtually stopped and sales were down to 15,400.