Here are my thoughts.
Normally with most pioneers and all cd players for that matter.
Its normally yeloow as your constant power,red as key on,black as ground,solid blue as a remote amplifier/cd changer,blue with white stripe as power antenna (same thing as solid blue wire though) (you can also tap into the key on hot as a remote wire if for some reason your remote wire channel was not operating properly).....speaker wires are as was stated above for the color combo's.
NOW....with you only having the 2 sets of speaker wires instead of 4 .....its either that the plug in ports for the extra speaker wires are on the cd players "plug" but had been ripped out at one point? or its a much older unit that was a 2 speaker unit and both chanels are blown and not pushing the juice out to the speakers because of that.
OR its an odd ball unit.....which I have seen alot of stock stereos use....and I will explain how to test it.
take a battery or a car charger...anything that will give you 12 volts of power supply......twist your red and yellow wires (constant and key on hot) together.....this will trick the cd player into thinking the key is on when its not even installed in a vehicle, touch it to the positive terminal of the battery.....then touch your ground to the negative terminal of the battery ...(this should atleast tell you that the cd player powers on and that part of it is good...(that is if you do not already know if it powers on)....from this point is where the "odd ball" part comes into play.......It may be a "common ground" system.....and the two sets of speaker wires (a total of 4 wires) are in fact 4 positive terminals (1 for each positive side of the speaker)......what you need to do to test this theory is take one of your wires and run it to the positive terminal of one of your speakers.....THEN from the negative terminal on the same speaker run a wire to the cd players ground that you connected to get it to power on....(you may be able to use a chassis ground aswell but for trial and error purposes run it to the stereos ground so you KNOW its grounded with the head unit).....thats should tell you if the stereo is any good or not and it may just be an odd ball older design.
Hope that helps and sorry for the long explanation ....I just wanted to try and give you as much info as i could....if that doesnt do it and it does not have any inline fuses for speakers (which would be odd if it did anyhow) than its most likely a junk stereo....BUT you may be able to open it up and find that it had been over heated and the solder points had melted somewhere and crossed ....in which case you could scap the solder out that is bridging the gap.....or you may find a burned copper band on the green board.
stereos are pretty easy to work on after you have done neough of them and know what to look for.
GOOD LUCK and let me know if what I mentioned helped ya figure it out!
