You've got to pull the demister completely out of the car then dissamsemble the demister switch completely. Putting it back together can be a bit of pain if you don't see how it comes undone, and usually the first time you take it apart it just falls too bits.
Phat Drift Damaged
Cobalt Blue 1994 EF XR8 5 spd
Fully optioned - Sunroof, cruise, body kit
Stock as a Rock for the moment