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I looked through all the pinpoint test for your system and they all point out to a fault radio (audio unit). You can either take it out and have the dealership send it out for repairs or find a replacement one and replace it. The unit itself is bad internally, that is why the stereo shop could not find out what fixed it last time. If all they did was play with the buttons, it is the unit itself. You can also check around and see if there are any repair shops in your area that can repair the unit. There is one other option, and that is to install and aftermarket stereo in the Mustang. But it sounds like you like the Mach 460, so it is your decision.