I recently bought a new stereo for my 94 gmc Sierra and it comes with one pre amp output port on the back of the stereo and my truck is a standard workhorse truck and only has four speakers, two in the dash and two in the back panels of the cab right by the passenger and drivers head and I was wondering if the rear speakers wires would be run through the wire harness or if they would have to be plugged into the pre amp output port?