I have a 1989 Jaguar XJS Convertible V-12. The cruise control worked when I bought it but after some time it stopped working all together. My gut tells me it is the cruise control switch on the console but many of the posts I have read seem to start with the mechanical parts of the system. Is it more likely the switch is bad? I should add that the switch for the driver's side window, close to the cruise control switch eventually failed also. Replacement of the switch replaced the window issue.

 

Mine works however the resume function of that switch does not and l have found the difference between it being on and off is microscopic switch movement, in my opinion the switch can go bad.

 

The switch supplies 12v to the CC module via the Yellow/Orange wire to turn the CC on, the resume side of the switch grounds the Black/Slate wire.

12 volts to the switch comes from the Light Green/Yellow wire.

 

I found a place to order the cruise control switch and another switch for the window. Unfortunately I got an email today that the cruise control switch is not in stock so now I have to find one somewhere else. It's a good thing I love this car.

 

Did you check the rubber bellows? The rubber can crack and leak vacuum causing the cruise not to work. Other fault I have found is the switch on the brake pedal shorted causing the cruise ECU to think the brake was applied, so wouldn't engage cruise. Yet another GM component that failed on my car.

I would start check the system electrically and make sure everything is working as it should, then test the vacuum components before throwing parts at it.

 

Before you go ordering parts and throwing them at the problem, I would do some fault finding. Do as Jb64 said and check the bellows holds vacuum, you can do this with a syringe and suck, and that both brake switches are ok, one is Normally Open (NO) and one is Normally Closed (NC), the NO also operates the brake lights so if the brake lights are working then this switch is OK, the NC disconnects power from the bellows solenoid thus dumping vacuum, this is the Yellow/White wire on the bellows in the engine bay.

Check the connections I said in my last post for the CC master switch.

 

Haven't checked it yet but it could bellows could be the culprit. The engage switch is a push button at the end of my turn signal switch but it doesn't engage the cc.

 

Also, with mine, I found that the linkage rod connecting the capstan to the bellows was the wrong length: there's a screw to adjust its length, and it's possible it may have slowly rotated more open over the months. Anyway, it's very easy to check.

 

The 89 doesn't have the rod connected to the capstan, it has a cable back into the cabin and pulls on the throttle pedal.

 

The seal on bellows on mine came loose. Where to buy replacement ?
Thank you

 

Try Jagbits. com.

 

Not certain as to these rocker switches. But, I've removed and cleaned mine to restore functions. A bit fiddly and easy to lose little parts. So, I work over a pan.


Carl