My ABS problems that I've had in the past have all stemmed from a faultly/damaged sensor. If the sensor has failed then it will throw the abs light on. If the sensor has picked up some rubbish from you from changing the discs and pads then that won't
help as it's a magnet that sends a signal from the toothed wheel that is near it. The other this that may be worth doing is cleaning the face that the sensor picks up as it gets covered in brake dust. lastly if you have reseambled it or knocked the sensor out of alignment so that it doesn't pick up the wheel or so that it rubs the wheel then you'll have a light all or which is worth checking in the dry.
Worth noting that if the light is on then the ABS doesn't function and you can easily lock the wheels