I have a 1983 F150 that is basically original. Recently my horn has started going off on its own. I drove a different truck to work today and my wife said the horn went off steady for two to three minutes then stopped on its own. I don't have cruise control, tilt wheel or a cigarette lighter. What could cause such a thing? I pulled the fuse for now. It was very hot today and the truck sat with the windows up ( black with black interior), could it get so hot in there the horn could go off?