All four of my instrument pack illumination bulbs had blown simultaneously. It was on a dark night in France at New Year and 700 miles from home. The four smaller warning light ones were OK and gave just sufficient glow to see the bottom half of the speedometer. I could see anything up to 50 mph or over 130mph!

When I removed the instrument pack to investigate yesterday, the four holders looked blackened as if the bulbs have overheated. Fortunately there was no corresponding marking on the instrument pack itself and the electrical contacts were clean.



Is this blackening normal? I can't scrape it off the holders so they have actually charred.

Jaguar don't list the bulbs separately and I had to take 4 x LJA4390BA bulb and holder assemblies. Given the condition of the holders, this was the best approach anyway.



Thanks to Reverend Sam for the video. This saved me loads of time by NOT removing the steering wheel as detailed in the JTIS procedure.

__________________
Graham
2005 XK8 4.2S Coupe

 

GGG;
It definitely appears overheating, electrical spike or short burnt out the bulbs. The major instrument cluster illumination bulbs are supplied electricity by the dimmer control module as are the other bulbs that are illuminated and can be dimmed by the dimmer control knob. Because the bulbs in the instrument pack that were burnt out are in parallel, it appears the problem isolated itself to the major instrument pack bulbs, and permitted power to continue to the other bulbs without harm. Did a fuse blow?
I would be somewhat concerned with the dimmer control module or why the bulbs burnt out.
Hopefully an isolated instance.

 

Jag13cat,

Thanks for the clear description of the setup.

A blown fuse was my first thought when it happened and I checked fuses numbers 4 and 14 in the Driver's side fascia fuse box - neither were blown.

I hadn't previously considered the dimmer but I now see this is protected by a 10 amp fuse number 13 in the Passenger side fascia fuse box. You're absolutely right I should be concerned about the dimmer module. The fuse is useless if it doesn't blow during a spike.

I'll keep an eye on it over the next few days and, if the bulbs go again, will swap out the dimmer.

__________________
Graham,
2005 XK8 4.2S Coupe

 

Fuses are for current spikes. This looks like a voltage spike making the bulbs brighten up until they cooked themselves. 12 volts is 12 volts, the bulbs won’t take any more current than their residence allows them to (V=IR), this looks more like 20 volts. Check you voltage regulator. A dead battery will make your alternator put out too much voltage unless the regulator has a over voltage cut out. My Moto Guzzi 1100 Sport didn’t have one, and when I bump started it with a dead battery it over voltaged and burned up the power chip in the computer, lots of smoke and a dead motorcycle!

A dead battery looks like a dead short to the charging system. The alternator goes ***** to the Wall!

The term used by pilots when accelerating quickly, the throttle is pushed all the way to the panel and the throttle lever (ball) actually touches the panel (wall). Hence, ***** to the wall.

 

Hi Bill love that expression when the alternator goes!!!! not heard that one before.

Cheers Al

 

Bill,

The bulbs are certainly all cooked and the holders look like burned toast

I'll check whether it still has the original battery. If so, at six years old it could be about to fall off the cliff.

How do I test the alternator?

Thanks,
Graham

 

Graham;
A quick test for alternator output is with a voltmeter (multimeter).
With the engine off and the voltmeter probes correctly pinpointed to the positive and negative terminals (not clipped on the cables around the terminals), your voltage reading should be around 12-12.8 volts at the battery.
With the engine at idle and electrical accessories off (no lights, a/c, heat, or radio) and the voltmeter probes connected as before, you should get a higher reading in the 13+ to 14+ volt range indicating the alternator is producing enough electricity to power the electronics and charge the battery.
As stated, this is a quick test without removing the alternator for a bench test in which a more complete test is performed.

 

the reason these bulbs have gone like this is because the wrong bulbs have been fitted ..they have tried to get more brightness or were the only ones they could get..my bet is that they are of a higher wattage than recomended and have cooked the bulbs and the plastic seround..if this was an electrical fault and the only one that could exist is that the supply voltage was to high ..all bulbs radio and many other diviced would be burned out..all power comes from the battery..so any high voltage say from a faulty alternator would be regulated by the battery..
fit the correct bulbs..job done

 

I've heard "***** to the Wall" has a much older origin - steam engine throttle control systems. These systems were regulated by a set of two spinning "*****" connected to a throttling mechanism. At low speeds the ***** revolve slowly on their axis and gravity pulls them down toward the ground. As speed is increased, they spin faster and centrifugal force causes them to rise perpendicular to the axis - toward the wall. When the ***** are "To the wall" the machine is operating at maximum throttle...

 

 

Yes, if these were replace with 6 volt bulbs this would be the results too. A higher wattage 12 volt wouldn't burn out the bulbs, they would run hotter though.

These all went out at the same time per his write up. Something happened to the power source. The only two power sources in the car are the battery and the alternator, unless there is some pretty fancy things going on inside the dimmer, normally just a rheostat.

 

Jag13cat,

Thanks for the info. I'll get a meter on at the weekend when I get back home.

After 180 miles with several stops and starts today, all bulbs are still OK

 

It is an electronic black box...not a rheostat.

 

dennisw and Bill,

The car was supplied and serviced by the same Jaguar Dealer from new, taken in PX and then sold direct to me. The PO put it into them for absolutely everything so the bulbs should be correct spec.

However, with the frequenct Jag parts canbe on back order with the factory, you never can be sure. I'm away from home for a few days but will check the old ones when I get back.

Pleased to report the dashboard is lit up like a Christmas Tree again this evening and the dimmer also operates correctly. Makes a change from reading my speed off the SatNav!

 

"electronic black box" - three words to strike terror into any Jag owner

Is it bolted to the top of the steering column or to the shroud?

 

Not the JagWrangler! More cool black boxes to open and mod.



Righthand corner below the dashboard in both LHD and RHD cars.

 

Enjoys black boxes. The man's mad - totally mad

Thanks,
Graham