Instrument lights


the green plastic foils are standard parts on Lucas instruments, so they should be quite easy to source. For repair you’d have to pull the instrument apart though. Maybe you leave that to the pros and postpone to a time when your tach needs refurbishment anyhow.

For the moment I’d just experiment with different types of colors applied directly to the original light bulb. - At least, that was what I did many moons ago when I made our basement my first party room … sigh … Today there are special glass colours; check out Pinterest and the like … or get another tach on ebay.

Good luck


75 XJ6L 4.2 auto (UK spec)

Indeed, or one can fabricate one with some plastic and maybe green paint, and just glue it in.
Taking the Tach appart is easy, I’m pretty sure that you just twist the bezel and it comes of, and two screws on the back. Just have to be careful, clean and no dust.

It’s not as easy as it sounds, if the bezel looks good leave it alone.

I took mine apart without any issues David. And more than once.

I don’t remember if I had to bend the bezel tabs, but even so having the VDP recessed gauges it didn’t really matter because it didn’t show.
It could be more problematic on the non-recessed dashboard though.

It can be, and the o rings can stick to glass and bezel, the bezel can corrode to the instrument, lots can go wrong.

There are coloured condoms for the bulbs. That should work.

Ink jet printer on transparent material !

Fellow lister made a lens for my CEL lamp. Looks OEM!!! Impressed my SMOG referee.


I swapped out the bezels - you have to bend the locking tabs be very careful. Once you do that the tach won’t separate, so it is a bit tricky to access the green foil.

Yet, beyond the paint-on-bulb solution David’s colored-condom-workaround sounds promising. Just, where did you find such small condoms, David?:wink:

When my red hazard indicator light once broke I fabricated a new one from an aluminium tube, cut the thread inside and die-cast the lower part with red plastic granulate. Just needed to put it all on a stove and it would make a wonderful handmade aluminium switch. No solution for our green instrument lighting though …



75 XJ6L 4.2 auto (UK spec)

Um… well… I… on ebay… ah… a Land Rover seller offers them! Saw them yesterday.
Paint would have to be very thick to do anything I think.

Bending the tabs can bend the bezel and chip the paint. Just twisting never worked for me.

WD40 or drop of 3in1 oil does the trick. Just slid the spring and bezel off and thinking it’s going to be easier to get back in the dash without ruining the veneer. I’m not going inside the tach. as I’m still interested in the T10 green bulbs but they have a spade connection. My existing holder is 1/2” round with a press fit and accommodates the screw in 2.2w bulb. Guess I’ll have to see if I can source a different holder, cut the wires and connect then blow out the green foil. Why do I do this to myself … I’ve got grass to cut !

One of the benefits of incandescent bulbs in the instruments is that the heat of the bulb is enough to warm up the air inside the instrument to remove moisture. I lived much of my adult life in southern California where the dry climate pretty much took care of moisture in my Jaguars instruments. I recently moved to South Carolina where it has been raining considerably since I arrived. Today I drove my 1990 V12 Vanden Plas all day in the rain. Pretty much all of the instruments were all fogged up from the rain over the past few days and noticeably fogged when I started out. After driving on some trips over the next few hours with the instrument lights on, most of the time in the rain, there was no visible moisture in the instruments. I plan to try driving the car without the instrument panel lights on the next time it rains to prove my theory that the incandescent bulbs do remove the moisture from the instruments, although I am pretty sure that is what happened.
LEDs never warm up and so they would not help remove moisture from the instruments.



It’s more about the dewpoint, Paul - when moisture settles on cold(er) surfaces. The humidity that air can hold depends on air temperature - as temps drop excess water condenses. In California, it may be hot, but the air is dry, there is little water to ‘wet’ the air as opposed to South Carolina. So the ambient air inside the instruments may condense on the glass faces if they are cooler. Which is likely the case with AC ‘on’ - or indeed over night. One point is that the air inside the instruments does not participate in cabin air circulation - which is dried by the AC…

All that said; your theory has considerable merit; no doubt the incandescent bulbs heat up the instruments - acting both on the glass, but also heat the air inside to ‘absorb’ more moisture. Certainly, LED produces less heat, which is the point - heat is wasted energy if it is visible light one wants…:slight_smile:

As the instruments are not air tight, they tend towards ambient air humidity - so a one-off instrument venting/drying is likely vain. Maybe with modern set-ups. made for LED, more attention was paid to avoid the problem?

Look forward to reports…:slight_smile:

xj6 85 Sov Europe (UK/NZ)

That’s a good point Paul, having experienced the fogging up problem my self.
On the Jaguar though I had leaking screens. Wonder if I will still have the same problem now that this issue is addressed.
On my little old Fiat as well, but it was not an example of perfect sealing either.

All modern cars though have LED instrument lights, I guess they control interior humidity better.

Paul, Frank, Aristides,
Interesting topic that I never had to think about.
Although my 86 series III has been in NY, FL and now in MA all the time with me , I’ve never had that problem or never noticed it.
PS. Back to original topic, I think I have found another nice tach. that I can use that will stop me messing around with my broken green foil.
Still like the bypassing of the rheostat idea and see if there’s a difference.

I’ve done so on all my oldie Jags. It as always worked for me.

A couple years ago I jumped on the LED bandwagon and replaced the instrument bulbs in my Series III. What a can of worms. “Brighter” lighting was easy. Getting a combination of bulbs that provided the same brightness in all the instruments was a real chore. I finally hit the right combination but it was effort I wished I had put elsewhere to be honest.



both my Spitfire and the Jag suffer from fogging (Smiths) instruments depending on humidity, temperature and storage.

No, any cars with “modern” instrument binnacles didn’t show anything similar, but the Smiths guages are not air tight and thus suffer from warm and humid air getting in and condensing inside the instrument glass once the temperature drops and air exchange isn’t warranted.

Usually the fogging disappears as soon as ambient temps get warmer or you turn on the heating.



75 XJ6L 4.2 auto (UK spec)

They probably put a heater in there! Along with a relative humidity sensor and control unit.

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Sealing instruments is difficult, even modern lamp housings are vented. It is true that LED lit instruments fog up (warm cabin cold instrument). I would not put LEDs into mine for that reason. Modern instruments don’t build up much condensation and I assume that’s actually because they are vented better than the old ones.

I would presume that any modern instruments designed by people who aren’t stuck in the past wouldn’t have any air space within them. They’d be solid. I still dunno why car companies insist upon LED taillights that are made just like the old incandescent lights with housings and reflectors. If I were designing the car, the taillights would be a peel-and-stick array of LED’s adhered to the outer surface of the body.

Laws and Common sense (often not the same).

Yes, they are called displays and if you haven’t lived under a rock for the last years (who hasn’t) you have seen them. Not that bad. I hate them but they improve. All stepper motor driven gauges have a lot of air space and I haven’t noticed seals on the shafts yet. Also many cars slowly collect dust between the plexiglass and the dials. Notably VW and Mercedes do it through the reset button.