I have just bought a 3 wire celing fan switch and I can't figure out how to wire it. It is a 3 speed fan and it has what appears to be a transformer with blue and black wires going from the old switch to the transformer. One black wire is coming out of the transformer to the plug. The new switch has a red, brown and black... can someone help?

Are the switches marked "L, 1 2" where the wires go? You just match that up. Both your switches should have 3 wires but you only mentioned two wire colors on the old switch.

What make/model is the fan?

http://www.ceiling-fans-n-more.com/ceiling-fan-pullchain-replacement-and-repair.php