Cruise control never worked on my '87 300sdl. Have owned car for about 4 years, looks brand new. This is the only thing that doesn't work on the car. All of a sudden it started to work today. Then later it stopped working. Could be amp, but suspect I should check some of the under the hood components. Any ideas? Anyone know how this system works? I suspect that switch controls amp and then amp controls actuator. How does system gauge the speed of car? When it started working it worked below 45 miles per hour. In fact it worked from the time I put the car in gear. I found this out by accidentally hitting the switch and car took off.