i'm trying to fit a JVC KD-G441 into my friends 2004 Punto, I can't get the CD player to work correctly it wont turn on, it will take a CD and spit it out again when pressing the eject button, I been told i need to have +12v on the red and yellow wire before it will work, is this just a matter of switching the red and yellow around? or is it more complicated than that

my JVC worked without having to change anything but you could try swapping yellow and red, and if that doesn't work, try joining them together.

join the red and yellow wire together