It couldn't be the Amp. They are powered when the ignition comes on. I just swapped in the Mach 460 from a 01-04 in my 93. So i know the wiring like the back of my hand. I have a few extra amps here if you want to try one.
part No's f7zf-18c808-aa
All the mach amps from 97-04 are the same btw, the older ones will work too, but I don't have a pat number from those..