As I want to narrow down what could be at fault with the cruse control I preformed this test:

Per FAQ. [John Sargent] The cruise control on 940s does not use engine vacuum but rather a vacuum pump.[Vladimir Ferdman] Apply 12V to the bottom terminal and GND to the middle and top terminals at the same time. This should activate the pump and the vacuum control valve at the same time and cause the servo at the throttle to contract. If the GND is removed from the middle, but left on the top terminal the servo should stay contracted and hold vacuum when the pump is off.

And it worked fine.
I also ran codes and got 1-1-1 all four times.
During a road test I reached down and checked the bellows (I left all the under dash stuff off so I could do this) as I switched the system on and the bellows only moved a little. It did not create a vacuum, never mind hold it and seems like the signal is getting there, but not nearly strong enough.
The wires which I could inspect in the stalk all look to be intact when I took that apart, so I still don't know what's going on.
Perhaps the computer unit is malfunctioning?
Perhaps the wires at the switch deep in the stalk are messed up somehow.
So it worked fine with a 12v direct feed, but only got a faint signal under driving conditions.
Any further testing recommended?
I do have a digital multimeter, although I wouldn't say I am really handy with it.
Thanks in advance.