Instrument cluster
 

After a short time the instrument cluster on my 1996 XJ6 completely illuminates, all warning lights flash on and off and instrument dials go haywire, the cars performance is unaffected? Can anyone advise what the cause might be? One garage diagnosed a faulty alternator which I replaced but the problem remains.

Instrument cluster disco lights
 

Thank you for your thoughts about the ignition coils, I will investigate and let you know.

+1

@countyjag is spot on and bad coil(s) is almost guaranteed to be your problem. To find some related posts and tips on diagnosing, type this in to Google

site:jaguarforums.com dashboard christmas tree

Brendan and CountyJag speak truth. Pull the coil cover off and then fire it up on a dark night and observe the coils as it idles. If any are producing visible light, as in a little lightning show down in the yellow goop, that'd be your culprit. "After a short time..." sounds like it may start failing after initial warm-up..so do the dark test at similar conditions as to when the IP flashes at you.

One thought is the fuse for the instruments comes out of the LH heelboard fuse box with it's king relay

You can swap that relay with the LH engine fuse box king relay which in reality only honks the horn

If you have a suspect coil the swelling if bad may be able to be seen as a crack on the thick cylinder and some have seen bad boot sections on the skinny part