If you said you have 4 wires at each speaker then you have BOSE sound system. That should be easily visible on the HU (a BOSE logo should be printed on the lower left corner of the screen).
Now if you have BOSE and you have just speakers in the back then you will not get sound no matter what (well you will have very low signal sound on two of the wires). The BOSE sound system has amplifiers behind EACH speaker so you need to see some electronics attached to the back of the speakers (that is the amplifier).
Now wire colors
ORN AMP +12V power supply
BLK AMP GND
(both sides 18 AWG wires)
LT BLU Audio + Left
DK GRN Audio Left
LT GRN Audio + Right
BLK Audio Right
(20 AWG wires)
But you should not worry about witch wire is what, they end in a standard 4 pins connector, once you have the correct speakers the connector only plugs one way.
Here are the BOSE speakers (notice the metal case thing, that is the amplifier. You can also see the connector with a piece cut of the car harness on the left speaker).
For more details see my BOSE thread
here (Stock to BOSE conversion).