why would my battery light flash on and off the dashboard when driving. on 1999 Volkswagen Passat

i have no power to electric front windows and peterol cover button, central locking not working. i have new battery and alternator and starter motor. 2 months ago.

Asked by for the 1999 Volkswagen Passat
poss defective alt or wiring. where did you get alt?
had fitted at an independent dealers but prob only started since then,will take back and see what they say. many thanks for the advice.