make sure your brake lights and parking brake works OK.
make sure brake fluid level is not dropping over a day or two. IF IT DROPS DOWN THERE IS EXTERNAL LEAK IN BRAKING SYSTEM.
If above things are OK, fluid is not dropping in level, then target following components in following sequence.
DO YA FEEL DIFFERENCE IN BRAKING AFTER BRAKE LIGHT STAYS ON, DO YA HAVE TO PUSH BRAKE PADLE MORE DOWN TO THE BACK-(FIRE)-WALL???
IF YOU TELL US HOW YOU BRING A CAR TO A COMPLETE STOP, PROBABLY WE CAN HELP YOU OUT.
1) AIR ENTRAPMENT : BLEED THE SYSTEM PROPERLY AND RE-TOP THE BRAKE FLUID. ALSO MAKE SURE ROTOR & PADS , and DRUM & SHOES are within minimum specification.
1) MASTER CYLINDER : internal leak in master cylinder fails to hold and sustain INTERNAL PRESSURE.
2) BRAKE POWER BOOSTER (RARE CHANCES)
3) BRAKE PROPOSITION VALVE (RARE CHANCES)