So after sitting for a week I took the Jag out, or rather tried to. The dam speedo stay at 0. Is this a fuse or...….

Thanks

 

Hi Malc

Sorry to say its looking a lot more like or...........

Now while its not a very difficult job, I cannot overemphasize how careful you have to be, or else you could ruin the Instrument Cluster completely, where nothing will work

This is how I fixed the Speedo which suddenly stopped working on my 1990 Pre-Facelift XJS with just a little or maybe a lot of help from the GF

Who is still insisting on taking all the Credit for doing this job and refuses to stop Smirking every time that the word Speedo is mentioned except of course when Smirking turns into Gloating!

And that's even worse!

But it might even be the little Black Box over the Top of the Fender/Wing in the Boot/Trunk or the Sender 'Thingy' in the IRS

If the Cruise Control works then it is more unlikely to be the little Black Box down the Passenger side of the Fender/Wing in the Boot Trunk (UK) Car

If none of those then here is the way I fixed my non working Speedo on Page: 76 of my 'Cherry Blossom' restoration thread

(The Formatting is all over the place from when they had a re-design of this Blogg)

How I fixed the Speedo on my 1990 XJS Pre-Facelift

 

In addition to the excellent advice from OB above, you can use your trip computer to help diagnosis the problem. Take the car up to a speed you are fairly certain you know what it might be, select AV. SPD. then press RESET until it resets.

- If it reads zero, the problem is the speed sensor on the diff.
- If it reads approximately the speed you expect, the two most likely candidates are the cluster contacts or the Speed Transducer in the trunk.

Good luck.

 

The speed interface unit has 2 outputs, 1 goes to the speedo and cruise control and the other to the trip computer, these outputs have a different number of pulses per mile and are from different outputs of the same chip in the interface unit so if nothing works then the problem could be either the speed sensor or interface unit.

There are zener diodes on the output of the speed interface. They are there to protect the output from shorting if these diodes are bad you will have no output. If you pull the speed interface out and measure the diodes with a multimeter put the leads on the diode one way then reverse the leads they will be short circuit in both direction if they are bad.

 

Thanks guys great advice as usual.

So l was away for a few days and thought l would take the car for a quick test drive. everything worked like it should. (Except the LED mainbeam )..…..Blessed by Lord Lucas of Darkness again !!!