All your speakers were powered by the head unit as a left and right channel only.. and if you ONLY plug in the harness without surgery at amp level.. they will still only be powered by the left and right channel of the new head unit. "plugging in" the extra RCA connectors does not connect them to anything other than the back of the head unit. Have you looked through the forum on the stereo hookups? You will find plenty.. including amp wiring and how to "4 channel" the setup.