If you are having problems, like I did, with your tach and speedo being off after installing new gauge faces then I have found the solution! It seems as though Ford had a device in these model years that reads your RPM's, speed, volts, fuel, oil pressure, and other things digitally in the trip/odometer display. All I did was get to the speed and RPM display and set the needles on the gauges accordingly. I hope this helps all of those whose gauges are off, I know how annoying it gets! Here's the link: http://www.mustangworld.com/ourpics/fcar/dtcodes.htm