[george kujanski]

My first thought would be that the connectors are loose; once they get loose, they will get hot, discoloring the plastic connector. Also, once they get hot, the brass terminals tend to lose their spring tension, propagating the problem.

Squeeze the terminals with some long nose pliers and see if the heat problems diminish. If not, there may be the same type of problem internally in the switch. A third possibility is that there is short in the circuits connected to the switch, drawing extra current, but this would tend to blow a fuse.