2004 Mustang GT Mach 460 Replacement Questions

What head unit did you put in there? Model number would help a lot. Also, what harness did you use? There are ones that 'work' and ones that 'work correctly'.

just do it rip it all out and replace depending if your guna run back speakers or not youll need a 2 channel or 4 channel amp(w/rear speakers) dual amp wiring kit, speaker wire, an rca cable for each set of speakers. speakers go 6.5 components in front with adapter plates you can either buy them or make them dont skimp on the front speakers buy a good set its very dependent on your taste but good brands are, image dynamics, cdt, focal, dls. i wouldnt skimp on the amp either. i run only a front pair of components when your siting in the front you never notice there arent back speakers and it keeps the sound stage in front of you. So if you can afford a good set of rears and 4 channel amp go for a good front set of speakers and a good 2 channel amp this way you get the good sound you want and you dont have to worry about your amp failing in a couple years.