Frank, if the wire simply fell off, that would not make the light come on. The wire had to find ground somewhere. That's what cuts the light on. When pressure gets too low, the sender switches and grounds the terminal the wire plugs into and cuts the light on. Unless the end of the wire hit ground and cut the light on, I would trace that wire all the way up to make sure that it did not fall on something hot and melt the insulation and ground like that.
