2002 mustang factory amp problems?

So, I bought a mustang last year and only the tweeters have ever worked,
well when I took the back seat out and checked the factory amps, they  were
unplugged so I plugged them in and still nothing, I've checked all the fuses in
the car and they were all good, are the amps blown or is it something else
since there haven't been any sound besides the tweeters? I should also add
that I replaced the head unit after plugging the amps in and still nothing.