im looking for a head unit from a 2003 or so mustang with a mach audio system in it... a buddy of mine tried putting a pionier h/u in with out knowing how much of a pita it was gona be to put it in... every where i checked said you need to completely remove the factory amp's and re-wire the speakers in the trunk and door pannels and bypass the speakers...

so he just decided to leave it alone and put the stock h/u back in ...

 

im pretty sure you can use another harness or somthing and be fine.. if you run aftermarket speakers then you have to re-wire