There was a post in June concerning hidden antennas. One possible unit was from the Chevy Lumina van. This sounded good but it is not what to use. The antenna is a tuned item meaning that the size is big enough to capture radio signals in the AM & FM spectrum. This antenna is bigger than the Mustang roof and trimming it to fit would compromise signal reception, you might not get all stations available. This is why it worked good in the poster's garage. The other reason why it won't work in a Mustang is because the Lumina is a plastic body and the Mustang is steel. The steel Mustang roof would act as a shield blocking out reception.