help needed oil pressure light
 

hi all i have a 1996 audi a4 1.8 20v turbo i drove it home with a faulty turbo and no other probs fitted a second hand turbo i know was good and the red oil light has came on so i put a oil flush in and changed the oil ( mobil 1 5-30 ) and the oil light still comes on when revved above 2000 rpm i have just changed the oil pump and strainer and oil pressure switch and the oil again and its still the same had the wiring checked and thats fine .............on the turbo side i fitted a a3 turbo cartridge could that be the problem or has anyone got any idea's input would be gratefull please