Speedo on 1988 V12 xjs

[skodajag]

My speedo has stopped working. From memory the speedos on earlier cars were cable driven but later ones like mine are electrically driven? Is that correct? Any advice appreciated on removal of the dash/speedo. Also can you tell me where the electrical take off points are for the speedo? I was wondering if it is worth checking the wiring before trying to dismantle. This because I hate removing dash trim, and risk upsetting other wiring on the way....

[davidr]

Hi there, as we've discussed before, your speedo is driven electronically by a sensor mounted on the diff casing. In my experience, your problem us more likely to be a failure of the sensor unit or the interface in the boot than the actual speedo head unit.
The speedo and the fuel computer ( and the cruise control) share this input. Are the fuel computer and cruise working as you'd expect?
Regards
David

[skodajag]

Thanks. Trip and fuel seem to be working ok. So I guess that points to the speedo head. Also other dash gauges, including rev counter are working fine so it definitely isn't the controlling fuse.

[skodajag]

David, you mentioned wiring in the boot. Can you advise what to look for, for example, the colour coding of speedo wiring? Thanks in advance.

[Brakebuster]

the speedo pickup comes off the diff , the wires come into the boot behind the spare wheel , and the sensor wire then goes up under by the fuel filler pipe, this then goes to a small electronic box that sends the signal to the dash

the screened cable( 2 core coax cable ) is known to break , so check continuity , also the diff pickup needs to be within 2 thou of the gear ring to work correctly , but this is very tricky to access with the rear cage in place

BB

[ptjs1]

skodajag,

As you've mentioned that the trip is recording distance, this points to the speedo or wiring connection to the speedo.

I would start by looking at the wiring diagram in the workshop manual,identify the speedo signal wire and then, after pulling the instrument cluster check for a signal on that wire on the wiring plug. If that reads ok, then it points to the speedo itself being faulty.

Paul

[Brakebuster]

lets not forget that the cluster is connected using a ' flexible circuit ' , these are known to break , also the signal to the speedo may well be fine, but the ground connection to the printed circuit may well be poor or intermittent ,

BB

[skodajag]

Paul .. Re pulling the instrument cluster: is it fairly easy to do this without disconnecting other wiring? I tried tentatively and there seems a fair amount of resistance to it coming forward....

[ptjs1]

skodajag,

The usual procedure is to adjust steering wheel to give as much room as possible. Then to tip the cluster forward which then allows a bit of room to get to plug connections at bottom of cluster. I'm sure BB will advise if there's anything different about your pre-facelift cluster.

Paul

[skodajag]

Thanks to all .. Got the cluster out without too much hassle and can now seen how it all goes together.. Now for some testing...

[Brakebuster]

if you have any ' green ' on any of the contacts, this will be the first place to start ,

use some lemon juice or buy electrical contact cleaner to remove the green corrosion , this can also be in the plugs that you removed

a quick spray with some ordinary hair spray will coat the contact with a fine varnish to help prevent it from happening again , you can also spray the battery terminals like this to stop them from corroding.....


next is to prove the earth / return / ground of the cluster, the ground is known to fail in several places including the main cable, a supplementary cable can improve things immensely

the main ground bar that is screwed to the back of the cluster also fails at the contact point of the flexi circuit , unscrew , clean and ensure you don't get the plastic insulating part in between the metal parts

other than that look for corroded or damaged circuit tracks on the flexi , the plastic separates and the circuit breaks ,

after that its the instrument its self that may have failed

luckily , these are relatively cheap on ebay , so you could buy one and use it for parts

good luck

BB

[skodajag]

Success! It was poor a poor connection, a combination of looseness and "green" contamination. So thanks again. Very rewarding to fix these things oneself. A Jaguar Dealer would probably have replaced the whole instrument panel....At the risk of going off topiac, albeit briefly, I had a problem with a ride on mower which I was quoted £350 to fix. I stripped the carb, cleaned out the gunge and cured the problem 100 per cent for zero cost....