[xj40] DASH LIGHTS STAY ON, ALL THE TIME, 1991 XJ40

Dash lights must be getting power some how. With the key off. I
pulled the plug connection to the dimmer/over ride switch. The
dimmer & switch checked to be good, but had no effect on the dash
lights. Would there be back feed from some source?

Also radio problems. radio worked for about 1 month after putting
in the code when I repaired the vehicle after sitting for 5 yrs.
Radio has power, but the buttons have no response. Even the AM/FM
button cassett change and speed, no response. Pulled the battery
souce off and re-entered the code. Won’t even take the code this
time,(buttons do not re-act).

Have no manual. How does the ‘‘sport’’ on transmission work? By
holding gears longer, or putting in more fuel? She really gets up
and moves, and handles good in the snow.–
JAGSTEIN
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In reply to a message from JAGSTEIN sent Sat 3 Jan 2009:

  1. Dash lights:

Have you read up on the subject in the archives?

e.g. Jag-lovers Forums - Jag-lovers

You mention that you ‘‘pulled the plug connection’’ to the
dimmer / override switch. Did you pull only one plug? There
are two 6-way connectors to that unit, a black connector
which puts battery power on to that unit (amongst others)
from fuse C4 in the right fuse box and a green connector
which provides ignition switched ground to the unit.

The instrument lighting circuitry is quite involved -
especially for a non-sparks like myself, but if you want to
study it to find the fault I can recommend the diagrams in
the JDHT CD-Rom JHM 1130.

  1. Can’t advise on the radio - sounds kaput to me and in
    need of examination by an audio expert .

  2. The ‘Sport’ button merely better optimises the
    transmission to the power characteristics of the engine. In
    fact, I prefer to call it the ‘normal’ mode, using it full
    time. That which is now called ‘Normal’ should be termed
    ‘Economy’ because that’s how it was first described by
    Jaguar before the marketeers got hold of it and decided the
    term ‘Economy’ was not in keeping with the best traditions
    of a Jaguar ‘luxury sports saloon’ car .

As you guessed, it merely holds on to the lower gears longer
to provide more vivid acceleration - it does nothing to
boost power to the engine or alter the handling
characteristics of the car.–
The original message included these comments:

Dash lights must be getting power some how. With the key off. I
pulled the plug connection to the dimmer/over ride switch. The
Also radio problems. radio worked for about 1 month after putting
in the code when I repaired the vehicle after sitting for 5 yrs.
Radio has power, but the buttons have no response. Even the AM/FM
Have no manual. How does the ‘‘sport’’ on transmission work? By
holding gears longer, or putting in more fuel? She really gets up


Bryan N, '91 Sovereign 4.0 L, RHD
Cambridgeshire, United Kingdom
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In reply to a message from JAGSTEIN sent Sat 3 Jan 2009:

Not sure if the 91 is the same as a 90 but…

Until I bought a new dimmer switch module, to make the
lights go out I would need to take my dimmer to the
position that you would hear a click.

For years I managed getting by using the trick above. Then
it got to the point that I had no lights at night so time
for a new module.

Once I installed a new module I also noticed that the
interior lights, heater, etc. would stay on at night. For
a long time they would be intermittent…on, off, on, off.

IMO the entire dimmer switch arrangment is a bit over
engineered. Why the rehostat isn’t the main/only
controling unit for the dash lights is beyond me. Instead
there is a $250 computer board involved. Go figure!–
The original message included these comments:

Dash lights must be getting power some how. With the key off. I


John 90 XJ40
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In reply to a message from John S sent Sat 3 Jan 2009:

Ouch…didn’t spell check or edit. Wish we could edit the
posts after we hit the send button.

The above paragraph means that the lights within the rocker
switches stayed on, not the interior lights or heater.–
John 90 XJ40
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Found the problem of the dash lights always on. After all these 7yrs. of driving the 1991 Jaguar xj6. Was using a toggle switch to turn off dash lights. Replaced the spot of the dimmer knob, with the toggle switch. Wired the negative wire that fed the dash (using a wire puller, to disconnect each wire out of the plug to find). It worked, but then would forget to flip toggle switch off.

Found a dimmer switch logic board/modual at the junk yard. Replaced it with the original and it actually worked. Putting the wires back to the original plug connector. This dimmer switch (very complicated electronics) is located on the left side of the steering wheel. Best removing the steering wheel and then the covers. It’s just below the turn signal and hi/low stalk. The dimmer switch logic board/modual unclips and slides out of slot.

Even though the dash lights now work. Turning the dimmer knob, the dimmer does not effect the dimming of dash lights. But I’m happy.

Hi, I’ve never looked inside a radio unit from an XJ40 but I do know that lots of similar units from that era had a small internal battery on one of the circuit boards inside. It was kept recharged whenever the unit was powered and in use, and I think it was used for things like Station and security code memory back up whenever the main battery was removed from the car. If that is the case, it’s a good chance that 5 years without any charge has degraded that battery considerably, and using the radio since has just finished it off. If you are keen to retain the original unit it would be well worth checking if it has one. I’ve seen some that are similar to button type watch batteries and are held in place with a sprung clip, and others that are cylinder shaped and have small pins on and are soldered into the board.

Sorry I can’t help with the dash light problem, I hope you get it sorted out soon.
Cheers.

John …

You posted, “Ouch…didn’t spell check or edit. Wish we could edit the posts after we hit the send button”.

Ah but you can my friend, you can.

Open your post then go to the pencil icon at the bottom right. Open it and you can then edit your post that used to be there in all it mikstakehood forever. I’m not sure if there’s a time limit on this feature but it works very well.