2002 Ford Ranger rear speaker wires

   I am trying to locate the end of the rear speaker wires on a 2002 Ford Ranger . I pulled the factory radio out of the dash and there are 15 wires connected to the wiring harness.   I am assuming 4 of these wires are for rear speakers behind the seats. I have searched in the factory cutouts and as much as I can around the dash and floor . Does anyone know or where these wires go after they leave the wiring harness behind the radio?

 I would like to upgrade the existing receiver so i can use 4 speakers and use a plug in adapter on the harness rather than cut wires .

  Thankyou in advance for any info you can give me .    Jimi

the four wires are 

left rear

pos =gray/ lt blue

neg = tan / YELLOW

right rear

pos =orange /red

neg =brown /pink

     Jon , 

       Thanks for the info.    

                                         Jimi