Disappearing needles.

[charles]

could it have been after that incident that the needles stopped being visible? Might you have disturbed something?

[Dave Plowman (News)]

Not really - they are separate units within the same outer cover. And as I keep on saying the same bulb lights everything - and the numerals are fine.

[Dave Plowman (News)]

It's just a white case. So possibly a reflector. Although some were beige rather than white, just to add to the confusion.

Yes - they are a V shape.

The only light guides are in the speedo/rev counter nacelle. They appear to be to even up the backlight to the numerals, which extend right round the face - rather than just being at the top as in the minor gauges.

[Johny B Good]

Getting back to "Square One", so to speak, can you clarify a point for us? I get the impression that this problem didn't "Happen Overnight". Perhaps you can describe whether this was a gradual deterioration or a more sudden change.

Until we know for sure which of those two scenarios applies, a lot of suggestions are going to be based on speculation leading to a scattergun approach to finding the right solution.

[Dave Plowman (News)]

Gradual. Very. If it happened overnight I'd have suspected a bulb etc failure.

[Dave W]

It seems there's a 5W "fibre optic lamp" illuminating some switches - is this relevant at all?

[Dave Plowman (News)]

No.

[Peter Parry]

Has the instrument voltage regulator gone on strike? The output is supposed to be 10V I think. The pointer would not have relied upon luminous paint so light is being lost somewhere.

[Grimly Curmudgeon]

[Dave Plowman (News)]

The voltage reg has nothing to do with the lighting. It's only for (some) of the instruments themselves - the hotwire types. Ie fuel level and coolant temp.

[Adam Aglionby]

rie Curie, The Radium Girls and Dalgety Bay...

And tipping industrial waste into rivers never did anyone harm either, fact s a bit thin on ground in Mr Campbell`s letter: "few radioactive particles from a beach"

"The total number of radioactive sources (particles) that have now been rec overed since the beginning of our investigation in September 2011 is signif icantly greater than 1,000. Of these sources, to date, five had a radioacti vity content of greater than 1 MBq of Radium-226 (1 Mega Becquerel = 1,00

0,000 Bq). " Scottish Enviromental Protection Agency

"nor by those at Sandside Bay near Dounreay"

Dalgety Bay is radium dial contamination, Dounreay Sandside is fuel rod fra gments, bit different:

.aspx

[Adam Aglionby]

Ruling out lamp failure and luminescent needles, leaves failure of light re flector or transmitter it seems....

[Johny B Good]

Thanks for the clarification. That leaves just a couple of possibilities, either the fluoresent/reflective paint on the needles has faded or (just an outside chance) a seperate tungsten filament lamp has dimmed due to depostion of tungsten vapour onto the glass envelope sufficently to completely blacken it.

The blackened bulb envelope scenario doesn't seem all that likely since such filiament lamps are under-run by design for panel/indicator illumination duty (25000 hours life time ratings being typically achieved) so the issue of evaporation of the filament should be virtually absent.

An outside possibility might involve the voltage regulator failing at full battery voltage for the lamp involved causing it to run at a much higher temperature than intended but I think you may have noticed the extra needlessly bright illumination of the needles very early on.

If you can actually get at _all_ of the lamps to check, such a condition would become immediately evident. Assuming this is not the case, it would seem to be a matter of repaining the needles with a suitable paint. Unfortunately, my knowledge of 'suitable paints' is only as good as my success in googling for relavent information on the subject.

All I can suggest is that you need a paint that has suitable fluorescent properties rather than phosphorescent (afterglow as used on modern analogue watch and alarm clock dials).

[Dave Plowman (News)]

I'll take pics of the spare one I have so you can see how it's constructed.

[Johny B Good]

Which is true and explains the slight nagging doubt I had when I mentioned it in relation to blackened lamps.

Anyhow, apropo of any dimming control for the dashboard lamps, they usually rely on a simple reostat rather than use a variable voltage regulator controlled via a similar looking high resistance potentiometer.

This, of course, does beg the question of whether or not you've overlooked a cunningly discreet needle illumination control. I usually only discover such discrete controls when someone else has accidently turned the brightness right down, leaving me to prod and poke at the most likely candidates until I _eventually_ touch lucky.

[Dave Plowman (News)]

Having owned the car for ever and being quite good at electrics, I even went as far as re-drawing the factory wiring diagram in colour to make it easier to read. So here is a screen shot of the panel lights schematic:-

As you can see it's pretty basic.

[Dave W]

Are all seven lights on?

[Dave W]

Is the inside face of the front facia surrounding the transparent parts meant to be reflective, e.g silver or white? It might reflect light back onto the needles.

[Johny B Good]

I see 7 panel lamps (typically 2.2 watts apiece - a total of just over 15 watt's worth, about 1.25 amps). I guess the otherwise redundent dimmer shunt is only there to reduce the maximum thermal stress on the dimmer rheostat itself.

Assuming the inclusion of a rev counter, you need a minimum of 3 or 4 of those lamps just to illuminate the tacho, speedo, fuel and temperature guages leaving the possibility that one or two of the remaining 3 or 4 being used to illuminate the speedo and tacho needles[1].

Have you been able to verify the condition of all 7 lamps? If they're all functioning ok without sign of any blackened envelopes, it would appear that the needles may simply be in need of a "refresh" of their faded fluorescent paint job (assuming any light guides, if used, are still properly in place). That seems to cover just about any possible lighting issues short of the condition of the needles themselves.

[1] Sometimes, when the speedo and tacho are adjacent, dial illumination can be provided from a single shared lamp located between the two.

[JimK]

/ I'll take pics of the spare one I have so you can see how it's constructed. /q

Spare what?

Jim K