I recently took out my Delco stereo (AM/FM tape) and replaced with a Kenwood KDCMP5025. I bought a harness because I didn't want to cut any wires, it has 4 places to plug in the wires coming from the factory and the other end is soldered to the Kenwood harness.
The top half is for one plug which looks like 2 plugs (black), it has the front speaker connections and the power/light stuff. On the bottom the gray and white connections are for the rear speakers (blue). For some reason my car had extra wires going to the 4th terminal of that harness. There was another plug that was plugged into the stock radio, but there was no connection for it on the aftermarket radio. I plugged all of the wires into the aftermarket radio and it works, but I want to know what that extra wire is for? BTW I don't have premium sound