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Radio Specialty brand 15 inch cable is used to connect the remote in-dash single CD (or cassette) unit to the head unit*. These remote units were found in a variety of 1995-2002 Chevy, GMC, Pontiac and Oldsmobile vehicles. If you are adding the remote unit, this cable is required. It was not present in vehicles that weren't equipped with the remote unit from the factory.
*Please make sure the head unit you are using is capable of controlling an auxilliary unit. You MUST have the 9-pin auxilliary plug on the back of the head unit. Even then, not all head units are capable of controlling a remote unit.