Also remember there are a few different types of windscreen available for the focus MK2 and MK2.5 which also have different rain/light sensors.
The version of the rain/light sensor you need depends on the type of windscreen that is actually fitted in the car. If you fit the wrong type of sensor the auto lights and rain sensor will not work correctly.
As far as i know there is a sensor for normally tinted windscreens with and without heating and there is a different sensor for infrared coated windscreens with and without heating. The infrared windscreens can be recognised by the IR logo on the windscreens.