Next on my list is the cruise control. Fuse is good, all switches on the steering wheel seem to operate, + and - both indicate faster and slower speeds on the digital display, cancel turns off the display..... but it won't hold the speed. I know somebody has had this before... What do you think?

 

Happened to me once when the vacuum hose came off the throttle body.

A vacuum leak like this is not terminal. The cruise function resets to working every time you cycle the ignition on off on.

If after a reset cycle, you were to turn cruise on, it will work until the first hill, which would then disable cruise when it tried to use that vacuum to force acceleration and nothing happens.

As I think about it, Yes it does display an error message on the dash display too.

Given all those details you probably have a different fault but I figure knowing this can't hurt. Hope it might help you track it down.

 

Would vacuum be relevant to 05 model?

 

By Model year 2005 Jaguar had eliminated the accelerator cable and the vacuum controls. The cruise control is controlled by the ECU.
If the cruise control doesn't activate holding any speed the the most likely culprit is the brake light switch. Since all of the dashboard monitors say it is ready to work then it is probably the switch telling the ECU you have applied the brakes and that will shut down holding speed.
The brake light switch is actually 2 micro switches. One to operate the brake lights and one to disengage the cruise control. Yours is probably faulty if it won't set at all.
The first step is always to read the DTC codes with an OBD scanner.

 

Sounds to me as though you've got the Speed Limiter selected instead of Cruise Control.
There are two switches at the back of the J Gate gear shift. One is the Sport Button for normal gearbox responses or, when the red led is lit, a more sporty gear box performance.
The other switch selects Speed Limiter when its LED is lit. With that, you use the steering wheel buttons to set a speed and you won't be able to exceed that speed unless you engage the kickdown switch. Press that button down, the LED goes out and Cruise Control should be awaiting your pressing of the Set button on the St Wheel.

 

OK - I admitted up front I have a lot to learn about Jags. The speed limiter switch was on (LED lit) - so I turned it off and tried to set the cruise control. The first two times I got a "cruise control override" annunciation on the panel. I think I was going too slow - after going above 40 mph it worked like a charm.

I will say it was difficult to get the ASL switch to stay depressed - maybe the switch is worn because it seems that 8 of 10 times it won't stay depressed (leaving the ASL on).

Thanks again for your help, guys - novice mistake.

 

There is a link to the owners manuals for most years in the Stickies if you didn't get any physical ones with the car. You might consider downloading the ones for your MY and reading through it, there are some odds and ends they explain.