The cruise control started working after my mechanic took a look at it last year, unfortunately it stopped working again after the autobox swap in april 2014, so for a year or so I have been driving without this nice feature.
Last week I finally got around inspecting the electrics, but everything looked fine. No sign of corrosion or bad connections anywhere. I removed the vacuum pump, which also - from the outside - looked good, but when I took the lid off the motor part, another truth was revealed as there was much corrosion on the outside of the motor, and the spindle could not be turned.
The second picture shows the drive to the membrane pump, which was completely stuck. In the photo, it has been soaked in WD40 and was rotating freely again
The third picture shows one of the two vacuum solenoid valves in the pump housing.
Final picture shows the pump with the part number visible. You'll notice that it has "Hella" stamped on it. It seems to be the same part used in some Volvos and VWs, except - annoyingly - with a different connector.
However, I have fitted the pump back, and now have a working cruise control. Wonderful
So far it has only cost me time and some very dirty hands, and some WD40
/Anders