If it is the same as the Focus, it runs a Smart-charge system, controlled by the ECU as Dojj says. The recall the Focus's (mainly ST170s) were coming in for was a 1-way diode in the wiring which was blowing. A lot of techies were getting told off as they were changing looms under warranty for £xxx instead of a 70p diode

BTW: the battery warning light is controlled by the ECU, not connected to the alternator on most Fords after 2003/4.