I proudly own an 84 euro 500 sel with 276k miles. The cruise control has not been working for awhile. I have replaced the servo and brain twice from what was supposed to be working cars. I know that the thick black wire coming from the speedo is attached properly. My CD-rom factory manual doesn't cover tech-tips on troubleshooting this system. Anybody a CC expert or know who is? Also I have noticed lately that when I am sitting at a stop light the oil pressure drops to 0. I have been putting it in N to keep some pressure there. I changed from 10-40 to 20-50 but there wasn't a difference. At 2000 rpm the OP gauge reads 30. Any advice?
Myron

 

For you CC problems go to site
http://www.the 12volt.com/default.asp?
Choose cruise control.
Very comprehensive instructions given.
Shan

 

What is the oil pressure at 1000 and 2000 rpm?
Sounds like mis-calibrated gauge. Install another one on the line and confirm it.