Im upgrading my guage cluster to one that has a tach but my ford dealer said they cant change the mileage. Where or how do i do that?[?|]

i dont know if you would need a flasher to do taht or not. i am not to sure...i am 99% sure that you need some sort of diagnostic tool or something

The Dealer can do it. Try another Dealer. A flasher won't change the Mileage. The Mileage is stored on the Cluster.