Diesel, you can blow any speaker if you drive it too hard. The problem occurs when you're driving aftermarket speakers with the factory amps. The factory woofers are 6 ohms and aftermarket drivers are normally 4 ohms. Less ohmage means more current must be supplied by the amp. In the case of the Mach 460, the amps aren't capable of driving 4 ohm speakers the way the system is configured.
FalconGuy, I don't advise using the factory amps and speakers when installing a new head unit. It's just too damn complicated that way since it's not just about using the right harness as you can see in the following link:
http://www.stangnet.com/Tech-Article...Head-Unit.html
It's really not too bad installing a new system. You can very easily use the factory wiring if you don't intend to use outboard amps. Each "tweeter" is fed a signal directly from the factory head unit. I just used these existing wires to send the full audio signal from each channel of the new head unit to each door and rear channel crossover which would in turn feed a tweeter and woofer. The crossover boxes were mounted in the doors behind the 5x7 drivers and in the back under the speaker enclosures (I have a convertible). Voila...you're done.
Btw, I'm in McLean.
