abs light is on

I just put rotors, pads and bearings in the front of this ranger and it is doing some funky stuff. When I start it, the brakes are hard and the abs light is on. I drive it and the brakes then become normal and the light shuts off. after just a little while the abs light will come on and the brakes will feel normal. However, if I were to shut the truck off and start it up again, then it does the same thing. It will do this over and over again.