The Nissan Path

I just bought a 97 path 4x4. I was told the master cylinder was out because the brakes hit the floor with no pressure. I replaced it and had a different mechanic bleed the brakes and the brakes were still loose. When the car is off they stiffen really well, and also find it strange that my rear brake light also seem to stay on all the time.

This mechanic now says its the booster, but I thought the booster goes out when you feel the brakes harden from what I keep reading. Should i bleed the brakes again to make sure theres no air bubbles or leaks? I would hate to keep buying parts because of wrong diagnose. Any helps is greatly appreciated.

If the brake lights are on with no pressure, it makes me think that the proportioning valve is not centered internally. Make sure you bleed the brakes in the proper order specified in the Nissan FSM. And, yes, a bad booster will give you a hard pedal, not a pedal that goes to the floor. Make sure you adjust the rear brakes (if drum brakes) and make sure there are no leaks before building.