Instrument lights

To say the instrument lighting in my XJ6 III is dismal is an understatement. I bought some 12v6w (I think - they are in the car). They shine white but seem to be no brighter than the originals that provide a green hue - now providing a total mess. Any ideas on upgrading so that I can see when doing 135

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Have you checked the rheostat, Derek

Frank
xj6 85 Sov Europe (UK/NZ)

6w could melt the green filters, it melts the opticell but you didn’t touch that. Move the rheostat frantically, see if you have a good ground, then decide on LEDs, my S3 was very dim too and unlike earlier jags I believe that this was so from the factory.

Hmm, did someone try 6V bulbs yet?

How would I check the rheostat ?

OK back to the drawing board … I’ll check the wattage.
But,

  • ‘green filters’ ?
    Do you mean shake the rheostat ? Not sure what that would do.

Also meant to say … how to change to LEDs ?
Thanks David

The rheostat is the dimmer and it’s just a coil of resistive wire. Sometimes you can improve contact between the wiper and the coiled wire by turning it up and down a lot. Even then it is a bit dim on full brightness…and the rheostat will never put out full voltage (there’s a modification to be done but I don’t know how much that would help).

Green filters are plastic and they could melt. Your instrument lighting would be white then, doesn’t look so bad but not all will melt the same and it won’t look good.

LEDs, two approaches: you can buy LED bulbs that fit or you put too much effort into it and install a led strip inside the large instruments. You will very likely lose the ability to properly dim the LEDs. But you will see again.

No, merely exercise it. turn cw and back ccw. many times. it may sweep away corrosion and function…

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Most leds will dim with the rheostat.
You need to get them the right way round in some cases to light up at all e.g.T10 replacements.

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Amply answered by others, Derek…?

Frank
xj6 85 Sov Europe (UK/NZ)

Just bypass the rheostat and you will see a vast improvement.
If you take appart the rheostat (easy) you will see that even at the brightest position the arm does not go all the way and there is still some resistance.
I soldered a little piece of brass and now I have plenty of light.

The problem with LEDs is that they have a very narrow angle.
If you want to go that way a LED strip would be a better solution.

Derek,

David was spot on, I’m afraid: 6 W produce enough heat to melt away the green plastic foil providing the colour of the instrument lights. Ask me where I know - the PO has “upgraded” from 2.2 to 3 W I think and he killed the green foil on one of the smaller instruments.

That being said, the standard lighting is absolutely sufficient for the instruments. When doing 135 you better care for your headlights than for your instrument lighting. In fact, the brightness is poor for the opticell powered parts and insufficient for the SII warning light cluster during daytime.

So, I suppose you might just try to bridge the rheostat and see whether there is a change; if it does, clean and exercise the rheostat as described. If you’re at the instrument light bulbs anyhow, measure the voltage and try a test light; if ground is poor or resistance high and there’s only 10.3 V at the bulb, it won’t matter whether you’ve got 2, 3 or 6 W bulbs.

Good luck

Jochen

75 XJ6L 4.2 auto (UK spec)

Gentle men, one and all !
This afternoon I retrieved the tach. It turns out that the bulb that I replaced the original with was 8w not 6w. Needless to say you are all right as looking inside I can see that the green cover has blistered at the end. That accounts for the instrument having white illumination. Having googled the dismantling of the trip info. fascia to inspect the rheostat and trying to tackle an improvement to that seems a difficult adventure !
Now to find a green ‘foil’ replacement (any ideas) and I’ll cut the 135 down to 70 ! … shucks I really did want brighter instrument lights.
Thank you all for input, Derek

You can put green lightbulbs

https://www.dronenewsw.top/index.php?main_page=product_info&products_id=454003

Thanks Aristides,
I’m following up to see if there is a screw in version of T10. Otherwise I’m not sure how to go about the conversion. Has anybody tried ?

Derek,

where is the rheostat mounted on SIII cars? On SII cars you only have to undo the underscuttle casing - very easy to access and remove; they look pretty much like this one https://www.ebay.com/itm/184360092914. Maybe Jaguar changed technology on the last cars equipped with trip computer?

Good luck

Jochen

75 XJ6L 4.2 auto (UK spec)

Jochen, Derek, others,
Attached are pictures showing the location of the instrument panel lighting rheostat switch in the Series III saloons from front and rear, and how I partially disassembled things in order to install a jumper to bypass that rheostat in my 1990 V12 Vanden Plas. This modification made a significant improvement in the brightness of instrument panel lighting at night because the instrument panel lights are always at their full brightness. In my opinion there is no need to install different bulbs like LEDs to improve the lighting, just bypass the rheostat.





Please let me know if you have any questions.

Paul

Thanks Paul,

as usual, you clarify a lot! The switch, as circled in red, looks pretty much the same as on SII cars. Just the position changed. SIII owners may find it easier now to remove the underscuttle casing. Then again, the center console panel may be a bit more awkward to remove.

Still, Derek, the rheostat is kept entirely separate from the trip computer and “bridging” it, as I suggested, is an easy job. Paul used a spade connector and some shrink tube allowing for a very safe installation and - entirely free from distruction - restoration of original function whenever desired. What is more, Paul confirms that “bridging” the rheostat improves the instrument lighting.

Good luck

Jochen

75 XJ6L 4.2 auto (UK spec)

Jochen,
Other family members driving our Jaguars regularly complained to me about how dim the instrument panel lighting was while driving at night. Since making this modification they commented how easy it is to see the instruments at night and that the instrument panel lighting is no longer an issue. This modification was so successful that I made a similar modification to our 1990 XJ-S convertible to bypass its instrument panel lighting rheostat and that resulted in similar improvements.
I am not sure why the rheostats degraded over time to dim the lights even at full brightness, but bypassing them has significantly improved the instrument panel lighting at night in both cars.

Paul

Wow Paul … great stuff. Nothing could be simpler than following the detailed pictures. I’m now convinced that this is the way to go.
My only issue now is to get the Tach. light back to normal. Haven’t dismantled it yet so hoping I can repair (glue) the green foil and put the original bulb back.
Thanks to everyone !
PS I did check the T10 green bulbs but they are the spade type and would require changing all the holders if that was even possible