Pathfinder brake problem
 

We are trying to get a 91 Pathfinder (4WD) with 260k miles drivable again,
and are having trouble with the brakes. The ABS light is on, and the pedal
pretty much goes to the floor. The brakes have been bled, no difference.
How do I determine if I have a master cylinder problem, or something caused
by the ABS system? We are trying to keep the costs down.
Thanks -
Brian