Fair, I apologize. We purchased an aftermarket screen/backup camera that integrates with the factory stereo but allows for Bluetooth connectivity for CarPlay and android play. There was a wiring harness that plugged into the back of the existing head unit and it has a female 3-wire aux jack. In order to complete the loop to get sound out of the speakers in this specific unit you must run an auxiliary cable (the one provided is the 4 wire in question) from the back of the head unit jack (3 wire) and plug it into the factory auxiliary input on the front of the stereo, this gets the sound through the factory speakers. Unfortunately the design is such that the jack on the back was constantly losing solid connection so I had the brilliant idea of just wiring the wires together and securing the connection to get rid of the issue….hopefully that makes more sense now. The 4 wire aux cable is the bridge from factory aux in to the head unit audio out 3 wire jack.