For 700R4 Transmissions w/Square 4-Pin Connector This high quality system can be used without the factory computer (ECM). This unit is electronic, NOT vacuum controlled. It reads speed of the vehicle through a sensor that attaches to the speedometer cable. Transmissions with factory internal speed generators must be converted to cable drive to use this unit. This system locks up the converter at a set speed and unlocks it when the signal generator senses the vehicle speed is below lock up speed or when the brakes are applied. This unit is set to lock the converter at 42-47 MPH and can be adjusted if necessary. Actual unit may vary in appearance from photo.