okay here is the deal take a small battery (aa) maybe and touch one wire in the harness you believe to be the speaker harness and put it on either end of the battery. Then one at a time take each remaining wire and touch them to the other end of the battery. Do this untill you hear a static or pop sound over a speaker. When you do the two wires on the battery are for that speaker. Now to be sure you get all your speakers in phase......there will probably be a common mark on all of the speaker wires this is usually the ground, or if you can see the speaker wires on the rear deck speakers maybe you will be able to figure out the pos neg..........Now for the power side ......get a test light or a meter, and probe all wires with ignition off the one that shows power will go to the constant wire or memory on the new deck, now turn the lights on and probe all wires again the one that shows power will probably be the illumination, turn the lights on and off to check, if the test light goes on and off when you turn the lights on and off that is the one, next find switched power by probing all wires remaining with ignition on, when the test light lights up turn ignition off and the test light should go on and off with the ignition. then check for ground, hook the ground lead to the constant wire and probe all other wires with ignition off when you find ground the test light should light up. Now you may have a wire or so left if you have a power antenna.......you will know when you give the deck power weather your antenna goes up or not.
Well try this and let me know how it goes