Brake Problems

On a 88 Ramcharger. We have changed out rearend. Put a 75 Modell dana 60 out of a dodge 1 ton. 4:09 gears. rebuilt wheel cylinders, new master cylinder,bled brakes about 10 times. Still can't get any brakes.
Brake Warning light stays on, on dash. Brake pedal is very spongy. Any help or ideas??

Only way it will stop truck right now is if you put in nuetral. As long as in gear it will only slow it down.