Classic/Antique Car Repair: electrical ground issue, ford mustang, cruise night

Question
I have a 1966 Ford Mustang that I am told has a ground problem. One day while leaving a cruise night I turn the key to the on position and all of the gauges traveled to the extreme right. I had not done anything to the vehicle that would have influenced this happening. I realize that the electrical system in this vintage car is basic however I could use some advice on where to begin to trace this problem. I appreciate your time on my behalf.

Answer
It sound like a gadget on the back of the instrument cluster called the constant voltage regulator may have malfunctioned or the ground to that unit has been lost. However if the ground has been lost your dash lights would probably not work either. Do they work? let me know and then we can go on from there.
Brad