why is my "Check Engine -ABS LIGHT -BATTERY LIGHT" ON?

What is your question?

I got me a 97 Buick Riviera Supercharged 3800 series II engine. when i got the car those lights were already on. the vehicle also had a bad pulley on the alternator so i got a new alternator itself and got me some new spark pluggs while i was there . everything works fine car rides smooth but my "abs light, check engine ,and battery light" are still on now keep in mind the battery light appeared after i installed the new alternator but the alernator has been tested various times and passed every test. if u could help it would be great ! thanks.