Yes they will fit, but when I was going to get one for my Son's '04 GT I found conflicting ads on just what years they will fit. Some ads said '99-'02 while others said '99-'04. So I called Autometer and talked to one of the Engineers about it. He said that they are having trouble with them working properly in some of the '03-'04's, not all of them though . He also said they were going to stop producing them for that reason plus there was not enough demand for them. He went on to say they work good on the '99-'02 but Ford changed the ECU in '03 and then changed it again in '04 making it more of a problem. He told me they have even contacted Ford about it but were not able to resolve why the problems were occuring.
It sounded to me like it was going to be a hit and miss situation, so I decided against trying it. I know some have had good luck with it but myself, I would not want to chance it on the '04's since Autometer themselves said it's possible for it to not work properly.