Cruise Control Help
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After you have checked the fuses I would test vacuum actuator. Use a syringe to pull vacuum on the actuator and ensure it holds.
After that check the connectors and wiring. Then either the CC module or the speed interface unit in the boot.
The speed interface unit has 2 outputs 1 for the speedo/CC and another for the TC as they use different pule rates, even if the speedo is working the speed interface unit could still be the cause of the problem, check the connectors on this as well. It is located on the left inside the boot up under the buttress.
After that check the connectors and wiring. Then either the CC module or the speed interface unit in the boot.
The speed interface unit has 2 outputs 1 for the speedo/CC and another for the TC as they use different pule rates, even if the speedo is working the speed interface unit could still be the cause of the problem, check the connectors on this as well. It is located on the left inside the boot up under the buttress.
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Hi
Well I won't pretend that I know how to Fix it as I don't but at least we now know what you've got
So next I will put up a Photo of where to find the Fuse and then let Jagboi or someone else take it from there
You'd be surprised how many times an iffy fuse can easily turn out to be the problem, as in my own experience
Some of those 'Aftermarket' ones sometimes have much Thinner Blades that don't make very good Electrical Contact
Even though they seem to be a Tight Fit in the Hole
![](https://cimg8.ibsrv.net/gimg/www.jaguarforums.com-vbulletin/1920x1080/img_5345_37e77bb2b94cab8dcae3346cb603f6ee4b02dff1.jpg)
The Dropdown Fuse Box Panel on the Drivers Side of a 1990 XJS V12 which should be about level with your knees
(5) 10A @Jagboi Should be the one you're looking for although for some strange reason its not marked on the Panel
Last edited by orangeblossom; 12-09-2017 at 09:41 AM.
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orangeblossom (12-10-2017)
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Mine is not working either but I have eliminated several potential culprits by doing the following:
Take the unit out and remove the control unit out of the front side of the bellows. Bench test it to see if the little plungers are working. If not try some JB Blaster or other lubricant. If they still won't work you'll need a replacement.
As for the bellows use some high temp silicon to seal both end plates into the bellows grooves to ensure you have a tight vacuum seal.
Take the unit out and remove the control unit out of the front side of the bellows. Bench test it to see if the little plungers are working. If not try some JB Blaster or other lubricant. If they still won't work you'll need a replacement.
As for the bellows use some high temp silicon to seal both end plates into the bellows grooves to ensure you have a tight vacuum seal.
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On a side note, there have been a few occasions where the cable has pulled out of the retainer and the retainer falls out. If you add a washer under the screw then the retainer can not fall out of the bellows.
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orangeblossom (12-10-2017)
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I have had several reasons why mine didn't work and they were all to do with the bellows. check the wiring that goes through the end plate the heat and years will have taken there toll on them brittle and break at the connectors. and bellows sealing is the biggest cause of failure.
Last edited by rgp; 12-13-2017 at 05:25 AM.
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orangeblossom (12-13-2017)
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