The switch was able to move past zero because the black plastic tab broke off. You'll need to glue someting there to keep it from happening again or you'll be going right back into the dash in short order. The easiest way to rig this is to glue a thin piece of plastic to the side of the piece which lights up and is inserted in the top of the wheel. Its the piece that the label "Fan" attaches to.

If that's too confusing email me offline and I'll try to give a better explanation.