It happened to my 70 about a year ago, cause....a heavy draw from an accessory, (new elect. fan installed w/o proper relay) moron rule number 1 always read the instructions. It melted all the way from the alt. wire, through the volt regulator, up into the dash harness, all the way up to the key switch. A sickning feeling. I replaced the entire harness after that one. I was very fortunate.