I have a 1986 560 SEL with a cruise control that works fine with the exception of "surging" when the car is going down hill. When it starts I disengage the CC, then activate it when the terrain levels out and everything is back to normal. I have checked the archives but can't find anything relating to this problem. Any ideas?

I'd say it is trying to tell you that you are going to SLOW. 560's like triple digit speeds!

It may help to clean and re-lube the linkages between the cruise control and throttle. They get pretty gunked up. Pop them apart, clean them, and re-lube with ATF or similar light oil.

Some CCs seem to just surge when not under load. You can try pressing the accelerator slightly--that'll sometimes eliminate the surge.