The color scheme from the old Clarion should pretty much match the
scheme of a new stereo. YOu really only need three wires from the old.
(+12v constant, +12v switched and Ground, if you have a power antena,
then there is a 4th). YOu should wire up the speakers yourself. You
need to bypass the fader.
Do an internet search and you will be able to find the information
needed for the wiring pin-outs. But, it is much easier to use a cheap
multi-meter. That is how I did it.
You should also look at replacing the old 6ohm speakers with real ones.