Flashing Abs Light?

i Have A 1994 Awd Chevrolet Astro, And When I First Got It I Saw That The Abs Light Would Flash On And Off At Times, Then Other Times It Would Turn Off Then Again It Would Turn On, I Had All The Rotors And Drums Changed Including The Brakes Because The Van Was In Need Of Them, I Thought Maybe It Was Some Time Of Error Or Somethin But The Abs Light Is Still Flashing, Can Anybody Help Me Find Out What The Problem Is, Could It Be A Sensor?