depending on which version you have, most newer fords have had the voltage regulator built into the ecu as of the past few years

we went through this with my mates focus with the alternator guy scaring him into thinking the ecu was buggered when the alternator was showing it was fubar
it was fubar and we swapped it over but the light came back on again in a matter of minutes
then went to ford to find out and thats when we found out about the wiring problems that loads of cars were coming in with

so make sure you get someone who knows what they are talking baout if you take it into ford about this, althoguh if the wiring in the wing has been damaged then it might be the cause, but then again, if the loom is run different on the ka to the focus then it might not be the same problem at all