Hatterasguy,
I had that problem on my 85 300SD. I used to do it once I started rolling in the morning, and would nto shut off until I turned off the car and then when I would turn it back on again, light was off again until I started to move it. Funny thing was it never shut off until I shut off the car. So, I got underneath the car and from the side facing the engine, I found the sensors. They are attatched with allen screws. I took them out, and you would not beleive how much metal shaving where attatched to it like a magnet. I cleaned it out and I cleaned out the hole it was in (found more shaving inside). Did both wheels just in case. Put the sensors back in there, lo and behold, no more light. I would take those sensors our, clean them out and replace them. In my case it took me 20 minutes to do it. Note that I had recently repalced both brake pades and pad senors in the front. I also replaces those wheel sensors and replaced brake pads and calipers in the rear. Now mine only has one sensor in the back mounted on the differential. But I am almost certain yours has sensors on all 4 wheels. It really is a very simple job, and you'll notice a difference in the pedal pressure once they are working correctly. In Florida ABS is not a luxury item.. With as many people we have on the roads (that should not be on the roads!)
Sudden stops are all too frequent. Good luck!!!