I had a similar problem and the rear of my switch had overheated because the
plug was cocked a little.  The plastic on the back of the switch melted and
pushed the plug off even more.  I unplugged the switch, scraped off the
melted plastic, and it has worked ever since.  However I think your problem
is burnt points inside the switch itself.  Check the fuse first but I really
think the switch is the problem.  Time to buy a new one.
Ken Wilford
www.VanAgain.com
John 3:16