The CTAMPPASSTHROUGH interface converts the high-level audio output of a new head unit to a low-level pre-amplified signal which will work with an amplifier. (Reduces the output volume from the aftermarket stereo to the factory amp) Use to install a new radio in a car that has an original fit amplifier that takes a pre-amplified audio feed. This lead has 8 way ISO connectors at both ends so if it is used on a car with different connectors (such as SAAB or Mazda) then you need to use the car specific lead as well. This might be a steering control or a standard iso audio cable. Can be used with car specific ISO leads for Nissan Bose, Mazda Bose, Honda Premium sound, Saab Bose or any cars with OEM low-level pre-amplifier signals from the original radio.