1988 lincoln mark vii abs light stays on and i have hard breaks

LEARNING ABOUT YOUR BRAKE SYSTEM
The hydraulic brake booster on a late model Mark VII and early Continentals, is very different from most. It is equipped with something known as a "TEVES" brake system. I'll attempt to teach you what does what and why, so you won't spend a ton of money just because you and maybe your mechanic aren't familiar how it works. The way its always been is,..."if you don't understand it...replace the whole thing"! The problem with using this technique is, unless you want to spend $2K for the whole thing, your going to be buying a used system....which may not be a whole lot better than the one you have now.
The main parts in the system that we will discuss include an ACCUMULATOR, a HYDRAULIC PUMP, a hydraulic pump RELAY, and a PRESSURE SWITCH. These are the key players in this operation.

THE LOCATION OF THESE PARTS ARE AS FOLLOWS:
HYDRAULIC PUMP MOTOR= Underneath the brake assembly (2 pin connector) Hydraulic pump motor
RELAY = On the drivers side strut tower
PRESSURE SWITCH = 5 pin connector facing the # 7 or 8 spark plug(drivers side)
ACCUMULATOR = Round black ball on the drivers side

WHAT THESE ITEMS DO:
HYDRAULIC PUMP MOTOR is an electric hydraulic pump used to "boost" pressure for the brake assembly. This pump is $900 new!
hydraulic pump motor RELAY is just what its sounds like. It gives the hydraulic pump motor power to come on.
PRESSURE SWITCH is the "brains" in the system. It senses how much pressure is "on line", and when the system needs more pressure, it tells the relay to "power up" the hydraulic pump motor.
Another one of its jobs is to turn on the RED BRAKE LIGHT, then the ANTI-LOCK lights to alert the driver that the pressure is dangerously low. (The reason the anti-lock light comes on, is because the ABS cannot fuction if theres a problem with the manual brakes)
ACCUMULATOR stores energy or pressure like a reservoir. Its there so the hydraulic pump motor only has to come on every 3rd or 5th time. Its design is more complicated, but basicaly the same principle as an air tank on a compressor.

WHAT NORMALLY HAPPENS:
Whats usually happens is, in time, the accumulator gets weak with age and can't hold the pressure like it was designed too, and therefore, the hydraulic motor comes on everytime the brakes are applied....rather than every 3rd or 5th time. This means all these parts are working 3 or 5 times more than they were designed to. This puts an extreme amount of pressure on an already old system.
What we know from this is, the accumulator needs replacement because its what started all this, but now the pressure switch and relay needs replacement also because it has worked it to *****.
NOTE: always replace the relay when replacing the pressure switch. The relay came on everytime the pressure switch told it too, so if ones worn out....the others not far behind!

ABS sensor in the brake hubs are bad, get a brake job.