I replaced the instrument cluster on my 89 XJ40 Vanden Plas with a rebuilt unit several years ago after complete failure of the unit. Now I have three problems that I suspect may be related.

1. From day one after replacement the voltmeter has read about 2 or 3 volts low. Battery test shows good, and volt meter check across the battery terminals is solid at 14 volts with engine running.

2. Temperature guage always seemed normal, including indicating temporary overheating while crossing the Arizona desert in mid-summer. After one major overheat a year ago I replaced the thermostat, the cracked fan and the broken fan shroud. Guage now reads rock steady 75 to 80 degrees. A mechnaic working on another problem says that the guage should read 90 degrees and that my (relatively new) thermostat should be replaced as it is probably stuck in the open position.

3. The cruise control system gradually failed completely since replacing the instrument cluster. It started by dropping out after running at freeway speed for 15 to 30 minutes. Gradually, this interval became shorter and finally the system will not even set. The trip computer PC board was replaced by a dealer and this temporarily corrected the problem to the 15 to 30 minute drop out mode. The dealer then swapped out, one at a time, all of the components in the cruise control system with components from an XJ40 with a working cruise control system from his used car inventory. No help! No charge, either, for which I am thankful.

Is it possible that all of these of these problems are related to the instrument cluster? Or, does anyone have any advice relative to any or all of these problems?

Looking forward to your help.

BobA
89 XJ40 Vanden Plas
72 E Type 2+2

Submitted by jam@ispwest.com on Thu, 02/02/2006 - 15:07

hi, this will not be what you want to hear, but I know of 2 owners with 1989 models and the same instrument cluster problem, one gave up and got rid of the car. But I might add that you have a very accomodating Dealer who has gone out of his way to help you, and at no charge. Most car owners don't want to deal with the dealer!. So my advice is to stick with that dealership, throw a tip at them, it doesn't hurt.

If you can do any tinkering or troubleshooting yourself, buy a Jaguar Service Manual for your car in CD form, (buy it from that Dealer, he deserves the business), and try to isolate the problem yourself, nothing is impossible with a bit of patience and logic. My Jags are 1984 and 1965, so I am not familiar with the XJ-40, but in my XJ-6, there is a separate Cruise Control "brain" or Module, which are known to go bad, and they can be repaired if not replaced. There is also a two or three wire Microswitch which is mounted in front of the shifter linkage which is part of the Neutral Safety Switch circuit. Can you start the car in any Gear other than Neutral or Park? If yes, you might need to replace the Safety Neutral microswitch, and that could correct the Cruise operation. In my car there is also a rubber Vacuum Bellows (looks like a round accordion), with two transistors and a Cable connected to the throttle pedal, all located in the engine compartment in a dedicated assembly. If your car has a similar arrangement, the rubber bellows might have been leaking vacuum as the rubber bellows deteriorated, until it no longer holds a vacuum, producing a no-start of the Cruise control. If that is not the issue, or if your system is different, the Service Manual might help you by showing the components and their locations, then testing each component will have to follow. Nothing is non-repairable. Also do some research in Jaguar forums, there's many Q & A sites that can help. Good luck!