In my shop I have an old Miller 250 AC/DC with high frequency start. It has a plug in for the high frequency start control going to the foot pedal. I can hit the foot pedal and hear it starting. However, I can't use the foot pedal to control the amperage. It just doesn't work. When I get my tungsten close to the metal, it starts the arc and then I have no control with the foot pedal. Anyone have any idea how to get this to work correctly? There is another plug with three prongs that comes from the foot pedal, but it doesn't plug into anything and was taped up to the current plug when I got it.