The auto-drive control unit is the brains of the operation. It's an interface which can control up-shifts into a split overdrive based on speed or rpm. Each Gear Vendor unit comes with this unit and it's a cinch to install cleanly under any dash. Since the 700-R4 already has an overdrive gear (4) from the factory, Gear Vendors used their dash switch delete option. Simply put, there is no AutoDrive (automatic engagement at cruising speed of the Gear Vendors like you would want with a 3-speed automatic). Dashswitch delete still gives you AutoLaunch for the automatic application of First over at the dragstrip and turns the overdrive off (if you have forgotten to) at low speeds so you always take off in First.