If you just want to put the sony in place of the factory head unit it should not be that much of an issue. If you want to use the speaker outputs from the sony you will need to run speaker wire from the head unit as the factory wires all run to the trunk. The antenna wire will need a long extension to run up to the dash to plug into the sony as well.
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'a stock car stereo is a beautiful thing to waste' MKIIa 60gb MKIIa 20gb