So I just recently purchased a 1992 XJS V12. A day or so ago the Speedometer quit working and I noticed the trip odometer wouldn't count up after I reset it to Zero. This then made me realize the odometer is not working either! Are these issues linked in some way, or are they isolated issues?

The ABS light was on when I purchased it and the speedometer was still working.

Thoughts/recommendations?

 

sd63141,

Does the car have a trip computer? If so, is the trip computer recording distance even though the speedo isn't working?

Paul

 

ptjs1,

yes the digital trip computer is recording the distance without the speedometer working.

 

Ok, so that implies the speedo transducer and interface units are working.

I'd start at the cluster as follows:

-check earth integrity to speedo. Consider running a separate earth wire for the speedo

- check integrity of wiring plugs to cluster

- check for continuity of current from wiring plug point terminal to speedo

Only after all that would I start doubting the speedo unit itself

Good luck

Paul

 

With apologies, not necessarily. The interface splits the transducer signal from the differential into digital and analog. Digital signal goes to the trip computer, analog signal to the speedometer and odometer. When my speedometer and odometer stopped working, it was the interface unit itself that semi-failed. It was sending the digital signal, but wasn't sending the analog signal.

So it could be the interface unit itself or contact problems with the interface connections.

 

Hi sd63141

Sorry to hear you're having problems with the Speedo but providing its not the Transducer which can be a PIA to get to

Fixing a non working Speedo can be easier than you think, or at least when it comes to taking the Binnacle out, which the GF managed to do with almost no help from myself (according to her!)

Here is how I (I mean She!) did it including Shed Loads of Photos:

Same procedure with 4.0L Six Cylinder Cars or ones with the small round dials
Removing and Fixing The Speedo on an XJS V12

 

Good point. Tks for mentioning that.

Paul

 

Hey guys thanks for all the advice! I’m pleased to announce after removing the instrument cluster and cleaning all the contacts the speedometer and the odometers started to work again. Thankfully it wasn’t anything more!

Until the next project, Cheers!

 

so jumping back on here because today I turned the car on and the needle for the speedometer didn’t even come off the peg. I reseated the two harnesses but it didn’t help. Thoughts as to why the needle won’t move?

thanks, Scott

 

My 1992 XJS just started to have issues with the odometers. Sometimes they work and sometimes they do not. Also, sometimes when the odometer does work the digits just spin at different rates. I had about 87000 miles on the car when this happened. Now the odometer shows 645012 miles. Tomorrow it will be a different number if I drive the car.

The speedometer, Tachometer, and trip computer all work fine.

I plan to take the cluster out and clean u pall of the contacts and make sure the ground is good. Two questions:

1. Do you think this cleaning process will fix the issue?
2. is there ea way to reset the odometer so that it shows the correct mileage?

Thanks for the help.

 

Just in case anyone needs to know the Speedo Interface is Passenger Side, tucked away down the inside of the Fender/Wing in the Boot/Trunk

Also Cleaning the Pins of the Multiplugs that Plug into the Tacho and the Speedo behind the Binnacle can get your Speedo and Tacho working again, just be very careful not to damage the printed Circuit

Lemon Juice does the Trick (@Grant)



Speedo Interface Unit Passenger Side tucked away on the inside of the Fender/Wing

 

Thanks for the info. If cleaning up the contacts and grounds on the speedo cluster does not work, I'll start working backwards to the unit in the trunk. I am hopeful that since everything works except toe odometers (which work some of the time) that there is just an intermittent contact in the speedo cluster.

Still curious if it is possible to adjust the digits on the odometer to the correct number once I have cleaned up all of the electrical contacts. I'll have to take things apart and see what is possible.

PS: I've enjoyed reading your posts on your project car.

 

Update: I removed the instrument cluster. Very easy. The one thing that i learned is to loosen the screws that hold the mirror control and the fog light controls. This allows easy removal of the bexel from around the cluster.



I then took out the main light bulbs as well as all of the nuts that connect the instruments to the flex circuit. This allowed me to bend the flex circuit back so that I could remove the white plastic housing from the back of the cluster. I did not remove the idiot light bulbs.



Then i was able to get to the odometers after unplugging the odometer motor from the pcb. I found that the main odometer has a white friction fit retainer disc on the right hand side of the odometer wheels. This is supported by a spring. In my case, thei disc had shifted to the right compressing the spring and allowing the odometer wheels to float around. Because the wheels were floating, i was able to set the odometer to the proper mileage. Then I slid the friction fit disc against the odometer wheels which allowed the spring to extend and apply force to the disc. Now the odometer wheels were tight against each other.
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I put the cluster back together. I ordered LED replacement bulbs ($40) and installed them. The 6 larger bulbs (Partsam T10 194 168 Dash Instrument White LED Light Bulbs Bright Panel Gauge Cluster Dashboard LED Light Bulbs 10Pcs/Set) that illuminate the gages were easy,


The idiot light bulbs (there are 20 of them - ), were a pain and very fiddly.


The larger bulbs are polarity sensitive. I installed them, then plugged in the cluster and turned on the lights. I got 5 right, one backwards. The idiot bulbs are non polarity sensitive which was good as they are difficult to install with a good contact. But, i can now see the idiot lights when they are lit. Great to be able to see the turn signals and the parking brake!

Installation of the cluster is straightforward. BUT, i learned one lesson. The speedometer needle moves when you rotate the cluster. By the time I got the cluster in place, the speedometer needle was at max speed.I had to take the cluster out and turn the cluster until the speedometer needle was pointing to zero. Then reinstall.

So, now all of the gages, speedometer, and tach work. The lighting is really much better on the gages, and the idiot lights are finally visible. Plus, the odometer works again. Unfortunately, i could not see anything wrong with the trip odometer and it still wants to randomly stop at xx.9 readings. I can live without that.