For some older cars being restored, a speedometer may be a bit of a challange and cost a chunk of change. While there are some companies than produce GPS speedometers that are simply drop in replacements, they can cost anywhere from $100 to $600. For a device as simple as a speedometer, there is definately a better way.
The first thing to do is to attach the stepper motor to the front plate. I made some brackets and glued most everything together.
The primary issue with just using a stepper motor is that witout a sensor, it can never know what position it is on. I added a photosensor (custom built) so that the speedometer can know what it is pointing at.