Abstract: An aftermarket device for permitting an electric solenoid of a torque converter lock-up clutch to be selectively actuated and deactuated by a vehicle electronic control module only when the vehicle is operating above a predetermined vehicle speed, or is operating in the high gear ratio. The device includes a switching transistor in the supply voltage side of an electric solenoid which enables the solenoid by coupling a source voltage to the solenoid from a brake switch. The switching transistor can either be an "NPN" or an "PNP" type depending upon whether a pressure activated contact switch in the transmission is "normally open" or "normally closed".