Morning all, from Stinking Hot Australia! (not that I'm complaining)

Bulb failure messages!  There have been so many threads about this or
containing this and other stuff.  I have such a problem and thought it
might be useful to bring the info to date together once more and seek
further info.  Apologies if this is old hat to some; it may hep others.

An important point to realise is that the bulb failure system on an XJ40
is very sophisticated.  The condition of all the external bulbs is
monitored *even when they are not on!*  This is achieved by a group of
computerised modules (someone described them as "one at each corner of
the car") keeping an eye on the resistance of the bulb circuits using a
very low current (and thus voltage, not on as in 12 V).  Any failed bulb
or circuit will not give a reading within the limits and the failure
module signals a fault, even when "off".  Of course, the iginition has
to be on in order for the whole system to be energised.

The small current used in this test is intentionally low enough for eg
corroded bulb contacts or even out of spec globes to give the failure
signal.  Dry joints in the BFM modules themselves can do the same
thing.  The most common cause is likely to be an actual bulb failure,
perhaps a side repeater, one of the number plate lamps, or a  bulb
overlooked in checking, such as the boot lighting.

So, the first thing is the check every external bulb (including reverse
lamps, blinkers and brake lamps)  and the boot lighting, that each globe
is OK, and then clean its contacts and the receptacle contacts. Note
that this must include the fog lamps on the rear.  If they are not
fitted to the front then dummy resistors are fitted in blank plugs.  My
plugs/sockets are yellow and contain normal 1 K 1/8 watt resistors (one
to each side).  Readings of 1K plus or minus 10% are OK - it's not that
critical because bulb filaments are not dead accurate anyway - hence the
reasonable tolerance.

I suggest all these things first, because working on the BFM modules
involves a little awkward dismantling and then a sure hand with a fine
soldering iron.  The modules are labelled "Bulb Relay Module" or
suchike.  They are a slab shape smaller than a paperback book and in the
rear they are bolted to the interior edges of the boot, behind the bulb
modules and behind the carpet.  One screw off the carpet and pull
forward to reveal the module.  After unplugging and removing the module,
straighten the tabs on the soft aluminium cover and prise off.  A
printed circuit board bearing relays and other components will be
revealled.  This board is notorious for "dry" joints.  If you are not
sure what a dry joint is, then you may be doing the wrong job yourself!
Any competent electronics enthusiast or technician should be able to
help.  Anyway, reflow suspect joints using a fine soldering iron.  I
think a check of the diodes with an ohm-meter is in order at this
stage.  They can be tested in circuit.  Should be a low resistance one
way - very high (or infinity) the other.  They are apparently 1N4007 or
similar.  Very cheap.  In an average of 50% of cases this will clear the
trouble.  Or else move on to the front modules.  They are similar in
shape and mounted just above and behind the headlamps.  Removal is much
more fiddly.  Disconnect battery negative (after being sure you have any
re-activation codes for the audio!).  For the right hand side, unbolt
and push aside the extrenal relay bank (A/C etc).  The bulb relay module
is connected by two easy to remove (one black one yellow) connectors,
plus a connector to the rear of the headlamp (fiddly to put back - just
pull off to remove).  One more connection and that is a black wire to
the earth, bolted to the frame.  It's quite fiddly to get to that and
handy to have a magnetic pickup tool to retrieve it when you drop it!
Note that there are other connecting tags to that bolt.  Should now be
able to unbolt and remove the bulb relay (failure) module.  Removal of
the cover is as before.  You will find that inside there is again a
printed circuit board, but also another mounted to the top as well.
This can be prised off and all contacts on both boards checked for dry
joints and once again diodes as well.  Replace cover and press in tabs
slightly as before.  Re-attach the earth wire (*very* important and very
fiddly), the headlamp connector (very fiddly - have to work by feel),
and then reattach the two connectors.  It's so fiddly that I think it is
worth checking after doing one, in case that clears it.

Apparently, the vast majority of bfm faults will be cleared by one of
the above.  Well, here's the rub.  I've done all these things and
*still* I have the rogue warning signal!  So, in case you were thinking
"he's obviously an expert" by now, you can see that I'm obviously not!
I  would appreciate any input beyond the above!

Hope the above will help some... and that someone will help me!

Regards to all
Alan