Horn Wire Falls Off

Pull the plastic cover off the wire terminal (it takes a tiny jeweler's screw driver to trigger the release tab), squeeze the terminal so it grabs the horn's male connector tightly, reinstall the plastic cover on the wire terminal and plug it back in. If you can't get the plastic insulation cover off the wire terminal, or, you think it will break doing so, either replace the whole terminal (with a new insulated terminal) or wrap the horn connector with some aluminum foil and then put the wire terminal back on over it if you want to do this on the cheap. Just make sure the foil doesn't short out against any surrounding metal.