Oldsmobile/Buick Repair: ABS SYSTEMS, abs components, abs systems

Question
My breaks became very hard & would not stop the car so I had the car towed into a shop, they told me that the abs system went out so I had them put in a used one because a new one was to expensive they say they bled the breaks. But the Yellow abs light won't say off it comes on & stays on for awile then when it goes off it dose'nt stay off very long what can I do to fix this problem ?" The car is a 1990 regency 98 oldsmobile V-6 3800 series motor.

Answer
I can't believe you would risk your life and other peoples lives by putting on a USED set of ABS components. Your LIFE is in that brake pedal and is must work each and every time you step on it.

Take it back to who installed it as the possible faulty part is numerous.