I've got the same problem.
Try this thread:
http://fordtransit.org/forum/viewtopic.php?f=54&t=112598You might be able to clean up the contacts, but it didn't work for me as they were too far gone I think..
I haven't bought another yet coz I don't know if a second hand one would be just as bad, or if the connect switches suffer from corrosion more because of where they're positioned.