do you not have any speake r wires connected to the radio cassette? do the red and black follow onto another plug which has more wires coming offf of it?
Usually red and yellow go to the red, black on black, and then 2x white for front speakers 2x grey also for front 2 x green and 2 x purple for rear speakers (cant tell you lefts or rights, youll have to work that out)
it would help if you have a good look around and put all the wire colours in your question.
good luck
Joseph, April 2007