First, let me start by saying, I think it was in 01 that ford changed the setup of the mach system. The earlier systems had a seaperate amp for the tweets (making the total amp count 3). The later systems used the head unit to power the tweeters. My guess would be that the wiring changed slightly too, wich is why you are having trouble with the plugs. that being said, if you have an 01+ mach head unit the tweeters will play without the rear amps, if not they may play but you will be sending them a full range signal (bad).