ABS light
 

I have a 1989 420 SEL the brakes work good if the dash ABS light is on But do not work very good at all if that light goes off ? Once the light comes on the brakes are very good , every time you start it,, the light may or may not be on / before the light comes on the brakes are noisy ? and hard to stop the car

Are you trying to tell us that the breaks (sic) do work well, even though the ABS light is on?
OR
Are you trying to ask if the brakes will work if the light is off?
OR
Both?

No. The brakes work only if the light is ON, Thanks

Were the brakes worked on, then this problem started happening after that?

no , they been worked on sance

Would you be so good as to provide us with your interpretations of the meaning of "brakes working", and "not working"?
AND
What work has been performed on the brake system?

rotors, Pads and bleeding , Thanks

When the brakes are working when the ABS light is on ,They work VERY GOOD , BUT when the light is off they make a lot of noise and it is very hard to stop the car scary

If the system was not properly bled, air may have been introduced into the ABS chambers. I would recommend taking your car to a professional mechanic and having the brake system properly bled.