1987 audi 5000 charging issue

[Eric Huppert]

ok so the battery light comes on a min or so after i start it . when you turn the igntion on but dont start the car the battery light does not light up like it should. if you rev the car up the light goes off and it drives fine and charges. this happens every time i drive the car when u first start it. i have replaced the voltage regulator and the exciter wire and the battery light bulb in the speedo. i am stumped and it is starting to get annoying  any ideas would be appreciated thanks alot. car is a 1987 audi 5000cs turbo.