Mercury - Gen I Throttle and Shift Cable 21 Foot Mechanical Engine Control. The Mercury Gen I Throttle and Shift Cable is designed for boats using Mercury mechanical control systems that rely on a direct, hands-on connection between the control box and the engine. Built for legacy Mercury Gen I control interfaces, it delivers a familiar, predictable helm feel without electronic involvement. The 21-foot (6.4 meter) length supports longer console-to-engine routing and wider hull layouts while help