1987 560SEL Anti-Lock Brake
 

Hello my anti-Lock brake light is on and will not go off. Does this mean that I am about to lose the system?

If the ABS MIL (malfunction indicator lamp) is lit then your ABS is not working. Now to figure out why.

The first thing to check is the OVP and the 10amp blade fuse on top of the OVP. If the fuse is good and the OVP has no ratle chances are it isn't your problem. Next would be to checking and cleaning the ABS sensors at the front rotors, the rear sensor is mounted to the differential and most likely not a problem.

Check the OVP first.

Abs
 

I posted this yesterday in a different thread. Since I realized that some revisions were necessary, I am reposting here.

Before changing the ABS unit, it would be a good idea to check the speed sensors which feed data to the ABS system. My 87 300D has 3. Do not confuse the speed sensor cable on the front wheels with the brake pad wear indicator sensor. One on each front wheel and one for the rear on the forward end of the differential. It is the only thing that is electrical that connect to the differential-at least on my car. Check them 2 ways. First pull the front wheels and look at the sensor cable. It hooks to a point forward of the shock. While you are there, it is a good idea to pull the end of it off the point where it connects-it is just one hex bolt-and remove all of the metal fragments on the actual sensor. It is a magnet and collects stray metal like you would no believe. Make sure that the insulation surrounding the sensor cable is intact. Taping to repair it is probably not an option. For the rear sensor, just pull it and clean it off.

Next measure the resistance on each of the front ones. The reading should be almost exactly the same for both. Before connecting the Ohm meter, remember to disconnect the other ends of the front two cables. One is just in front of the battery and the other is somewhat near the master cylinder (on my car). I think that they are brown cables with black connectors.

Finally, I am sure that you know this, but, just in case, an air bubble in the brake system can cause that light to stay on. Bleed and fill the brakes.

Thanks I will try both suggestions.