Xantia full beam headlights not working

[Dommo]

Hi all

Does anyone know whether there is a specific relay that engages the full beam lights on a Xantia? I've read in the owners manual that the headlights are on individual fuses under the engine bay fusebox, I figure it is unlikely for both full beam lights to have failed so am I right to think there will be a relay lurking somewhere? This is on my '96-'97 Activa. The full beam tell-tail on the dashboard still lights when I try and flash someone but the actual bulbs at the front of the car don't light.

I did find this thread regarding a similar issue, but I can't open the links, Jim have these disappeared?
http://www.frenchcarforum.co.uk/forum/v ... hp?t=25026

Thank you.

[RichardW]

I figure it is unlikely for both full beam lights to have failed

Possibly, but it's the most likely cause, so I would check them before you go on a wild goose chase only to find they are both knackered

[CitroJim]

I did find this thread regarding a similar issue, but I can't open the links, Jim have these disappeared?
http://www.frenchcarforum.co.uk/forum/v ... hp?t=25026

Try them now Dom,

I have fixed the links..

Sorry for the delay I was out all yesterday...

[Stickyfinger]

IF the cross over wires have gone.....don't bother fixing them.
Just make a new loom for the lights and take the opportunity to do the "headlamp mod" adding bypass relays and new earths.

http://frenchcarforum.co.uk/forum/viewtopic.php?t=52577

[Dommo]

Sticky - I have done that mod on my white VSX already so know it is a good idea to do. But I would like to fix the stock set up to buy some time if it's something simple.

Thanks Jim, I'll have a look at the pictures now. I tried reading the voltage at the bulbs last night but unfortunately I discovered that my multi meter no longer works, I think the leads are damaged I did look at the bulbs however and they don't look to have any damage on the filament at all. I'll try checking the voltage with one of my dads multi meters next time I see him.

Thanks guys.

[elma]

You can buy replacement leads for a multimeter fairly cheaply.

[Dommo]

So it would appear that while both bulbs look PERFECTLY intact, they were in fact both blown! Who'd have thought it?

And my dad has repaired my multi meter - the connector had fractured off the main board so he resoldered it back on for me.

Cheers chaps.

[CitroJim]

So it would appear that while both bulbs look PERFECTLY intact, they were in fact both blown! Who'd have thought it?

Seen that a few times now Dom, in all sorts of bulbs... Mainly in small ones...

Bloody frustrating isn't it

Still, delighted it was a simple and easy fix!

[Dommo]

Certainly is frustrating Jim - it's great that it's a simple fix but I really didn't expect both full beam bulbs to look perfectly OK and both have failed at exactly the same time, very odd!!

[CitroJim]

I had exactly the same thing happen to me on a Renault 4 in 1980 Dom. The difference was that car had 6v electrics and the bulbs were ordinary tungsten...

Never found a reason.. Like yours, maybe just old age and coincidence...

The only car I've owned with worse lights than an XM but only marginally so

[Stickyfinger]

Do bulbs fail sooner if run at a lesser voltage than designed for ?

[Hell Razor5543]

Bulbs tend to blow as they power up. I know somebody who built an advanced audio linked lighting system, that could very accurately track stereo sound placement, and different colour lights for the bass, mid-range and treble tones. At first it would eat light bulbs like they were going out of fashion, so he scratched his head a bit, and then added a little tweak to the program. When the unit powered up it switched on a low power feed to the bulbs, so as to keep the elements warm. This meant that there was a huge drop in bulb failures, as it reduced the thermal shock.

[elma]

Do bulbs fail sooner if run at a lesser voltage than designed for ?

Not in my experience.

[CitroJim]

James (HR) Yes, a soft-start is an excellent idea for extending the life of anything with a filament in it... Often in valve heater chains a thermistor will be used to achieve the same as your friend's software did...

Most household incandescent bulbs blow immediately on switch-on...

James (Elma) Yes, under-running helps enormously. It's why I always keep my Xantia dash bulbs dim!

[white exec]

Modern stage lighting almost always uses filament pre-heat, to avoid bulb failure during critical performances.
Reason bulbs blow on switch-on from cold is simple: a tungsten filament's resistance increases with temperature, like most (but not all) materials. So, when it's cold, a large current rushes in; when hot, the resistance rises and limits the current to the proper working level. Pre-heating (feeding enough voltage in so the filament is hot, but not producing visible light) gets the resistance up, gently, to approaching working level. It also makes sense for things like old-style traffic lights, pre-CFL and -LED.

Reducing the voltage on a tungsten lamp by 10% increases lamp life by 400%, iirc*.
Over-running by 10% reduces lamp life to 85%*.
*Long time since I looked this up; do check.

"Long life" tungsten bulbs are usually simply made to run at maximum on a higher voltage (eg 250v), and so in normal use are "under-run". Decades ago, both British Rail and NCB (coal mines) had a requirement for long life lamps for tunnels and other inaccessible places. The approached the big lamp companies with their requirement, but the companies declined to offer a product. BR, NCB and London Transport resolved to set up their own lamp production factory, at which point the commercial lamp manufacturers capitulated. Thus was born (among others) the famous British Home Stores "Long Life Lamp", from my father's company, Crompton.

If replacing small lamps in instrumentation and dashboards, always go for 14v items, not 12v. Alternatively, simply make use of the dimmer!