The cable is used to lock out the overdrive. The OD itself is engaged electrically by a solenoid.
When locked out, the OD is not part of the drive train and you can engine brake on deceleration like a normal standard transmission.
When the OD isn't locked out, the drive train will free wheel on deceleration. It will only go into OD when there is voltage to the solenoid.
Sent from my SM-G930V using Tapatalk