I would start by having the fault codes read from the ecu. That might give a clue.
Then check whether or not this is an actual ecu problem, and if so check if the ecu can be repaired. Repairing might be cheaper than replacing, it is certainly easier.
Have you seen this: http://www.petercoopercarrepairs.co....t_charging.htm

When done properly on some makes, the ecu can be replaced by a second hand one.
I am not sure if that's the case here, but that would involve the help from a dealer or someone with Ford equipment.