Presumably you mean the permanent dust extractor in your workshop?
Either buy a new switch and replace it or - bypass the existing switch (join the wires together with an insulated terminal block) and arrange external control - i.e. pull the plug or throw the switch on socket plate.
A more professional alternative is to make your own external switch box with parts from an electronics store. You will need...
Small plastic Box
Toggle, Push or Rocker Switch (illuminated rocker is good - all sorts of colors)
Two cable glands - one in and one out
Connection cables
Say $20 and two hours maybe...
Good luck...
Peccavi
June 2010
Automatic Answer
We may have found other answers which could help you.
howtomendit.com for free repair help, information and advice.
Try fixfault.com to fix circular saws.