2003 Ford Fiesta

Electrical problem
2003 Ford Fiesta Manual 47000 miles

fiesta zetec 03 reg 1.6petrol
my battery light came on the garage tested the battery and the alternator and said it was the alternator overcharging at 16 when it should be 14. They replaced the alternator but the next day the battery light came back on. They then fitted a new battery, I drove away and the light came back on? They are now saying it could be a wiring fault. Have you any ideas what the problem could be? They dont seem to be finding the probelm. And I know its not common for alternators to OVER charge? Please help thank you.
October 29, 2009.

Could be a wiring issue or a fault on the PCM. Have the vehicle plugged into a doagnostic computer !

System consists of generator, integral voltage regulator, battery, warning indicator, related fuses and wiring. Warning indicator illuminates with ignition on, engine off as a bulb-check. The Powertrain Control Module (PCM) simultaneously controls and monitors generator output. The PCM is able to increase idle speed when current consumption is high or the battery is discharged. To minimize engine load when starting, PCM prevents generator output until the engine has started and progressively increases generator output.

Dave H
Oct 31, 2009.