was the ABS light on before the brakes were changed? If not then you may need to bleed the brake again and again. If the light was on before then you will need to take it the the Ford Dealer and have them put it on there tester. I Had a 93 Ranger that the ABS light came on and stayed on. Took it to the dealer and it was the ABS Control Valve
Were the rotors replaced during brake work? Make sure they have the slotted trigger rings like the originals for the sensors to read. Also check the sensors to make sure in place and not dirty and have a good electrical connection. Does speedo act up along with abs light? Could be speed sensor in rear axle. Also I have read that the light for the passenger air bag shutoff switch can fail and trigger the light.