Why do you need to replace the on/off switch?
How can you tell it's bad if you can't get to it to test it?
Before you mess around with it just try cutting the plug and 6" of cable from the end of the cord - throw it away and fit a new plug - cheap, quick & easy.
I have fixed about half a dozen cleaners this way and have never had to replace an on/off switch.
Of course - you may have a bad switch.
Good luck...
Peccavi, June 2013