abs light on ,when brake pedal depressed , rear brakes lock up

Here is a good read on ABS brakes, I have a feeling you bleed the brakes wrong and bleed fluid back into the sensor...http://www.popularmechanics.com/ca rs/how-to/a461/2265091/

It is critical to follow the procedure when bleeding the brakes after a rebuild.

You need to all 4 brakes

You need to bleed all 4 calipers make sure you keep plenty of fluids and bleed all 4 lines to you get a steady stream out of each one of them starting to the closest caliber to the master cylinder which is usually the driver tire then take the positive cable off your battery for about two or three minutes hooked back up and light should stay off