This is what the schematic in my manual says.   The book is for a 1987 Firebird,  should be the same. May be easier if you did it this way 
http://www.crutchfield.com/App/Produ...677&c=3&tp=736
C1 
     E - Pink - Antenna    
     f - yellow - power 
     G -  Black - Ground
     M - Gray - radio back light
C2 
    A  -  Lt. Green - RH Front speaker
    B   - Tan - Lh Front   
    C  -  Dk. Green - Rh Front speaker   
    D   - Gray - Lh Front
C3
     H - Brown - Lh Rear   
     J - Dk. Blue - Rh Rear
     K - Yellow - Lh Rear
     L - Lt. Blue - Rh Rear
C4  
      A - Orange - Clock Power
      B - Brown - Display Dim Signal