Like most owners of early XJ40's I suffered with the Bulb Failure Module
problems and that accursed huge flashing warning light.

Again like most XZJ40 owners I searched the newsgroups and avidly read up on
the issue on www.jag-lovers.org only to find a heap of info, some good and
some not so helpful.  These BFM's really can be a pain and isolating which
one (or more than one) that has failed is troublesome to say the least.

On my travels I did learn something that may be of use to others and which I
had not come across elsewhere.

My XJ40 is a UK 1987 3.6 Sovereign with the large rectangular headlights
although this might be appropriate for other varients of the XJ40.

As all of us who have experienced this problem know, there are 4 BFM's, two
at the rear in the boot (one each side in the wings just forward of the
light clusters) and two at the front (one each side of the radiator just
backward of the headlights).  It seems that is more often than not one or
both of the front BFM's that fail, partly I guess due to their relatively
exposed location and also because they are more complex than the rear
modules, the fronts having two circuit boards one piggy-backing on the
other.

Assuming you have already removed and cleaned all bulb connections
(including the side repeater bulbs) BEFORE you go removing the front BFM(s)
to attempt a resolder job have someone turn the lights onto position 1 (i.e.
side - parking - lights only).  The Sovereign with the rectangular lights
were designed to illuminate the small side lights in the front bumper and
also have the main 60/55 headlamp bulb run in a dimmed mode at the same
time.

When the light switch is turned to side (parking) lights both the headlights
will flash momentarily as if being turned on and then immediately operate as
dimmed lights.  If either tof the headlights do not light up in dimmed mode
then you can be fairly sure that it is that respective front BFM that has
failed.

If I knew this when I started out I would have saved myself countless hours
replacing bulbs, soldering etc.

Bye the way Dave Manners in Wolverhampton (UK) sells reconditioned front
BFM's for about £145 a shot.

Hope the info may be of use to someone else.

Andy