So once again my old nemesis the infamous �Bulb Failure� light has
raised it�s ugly intermittent head. It will flash on for a few
second every trip or so.
I�ve done my due diligence and checked all the bulbs and their
connections and am convinced that the fault lies with one or more
of the modules themselves (I�ve resoldered the two rear ones
several times in the past). It used to be that when the �bulb
failure� light illuminated (in the VCM) I could detect which module
was acting up by trying the turn signals. The side that flashes
(clicks) at double speed was the culprit. Lately this little trick
isn�t working and both sides flash at normal speed�.argh!
Looking at the wiring schematics it shows that all four modules
have a pink/gray wire (among all the other wires) coming out that
eventually join together to provide a single wire input into
the �warning system� (which I can only guess means the VCM).
Could it really be that easy to just find that single pink/gray
wire going into the VCM and disconnect it to kill the signal?
To test this theory I removed each of the four light bulbs in the
left rear light assembly one at a time. Each time I removed a bulb
the bulb warning in the VCM came on as expected. I then cut the
pink/gray wire coming out of that module. When I removed the �tail
light� bulb… no warning, then I removed the �reverse light� bulb
and again� no warning (hey I may be on to something here). But
when I removed either one of the �stop/directional light� bulbs I
got the warning on the VCM!
Curses, foiled again. Somehow a signal is bypassing my little
friend the pink/gray wire that I cut and still feeding that info to
the VCM.
Is there no way to bring this beast of a system to it�s knees??–
Groove, 1989 XJ6 3.6L
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In reply to a message from Grooveman sent Tue 19 May 2015:
Dennis,
Had a similar intermittent BFM warning once. Drove me nuts
because all the bulbs were lit OK whenever I checked. Then I
gently tapped each bulb with my finger until I found one
which became open circuit for a second due to one end of a
filament temporarily becoming detached and that triggered
the BFM warning as it should (BFM doing its job again!)–
The original message included these comments:
So once again my old nemesis the infamous �Bulb Failure� light has
raised it�s ugly intermittent head. It will flash on for a few
second every trip or so.
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In reply to a message from Grooveman sent Tue 19 May 2015:
When I turn on the running lights, I get a bulb failure on
my 89. Same with headlights. After walking around the car,
I noted no lights out. But when I step on the brake, the
bulb failure goes out. Very puzzling. I think it may be
one of the license plate lights – that’s the next to check.
It is a goofy system.
If you look at wiring diagram 12, you will see that the bulb
failure requires 12 volts at pin LB54-32 (pink/gray). Fault
condition is grounded (or open). I’m thinking a switched 12
volt supply spliced into the pink/gray wire at the VCM would
put the bulb failure alarm to sleep for good.–
The original message included these comments:
So once again my old nemesis the infamous �Bulb Failure� light has
raised it�s ugly intermittent head. It will flash on for a few
second every trip or so.
Could it really be that easy to just find that single pink/gray
wire going into the VCM and disconnect it to kill the signal?
Curses, foiled again. Somehow a signal is bypassing my little
friend the pink/gray wire that I cut and still feeding that info to
the VCM.
Is there no way to bring this beast of a system to it�s knees??
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In reply to a message from Jaguarpete sent Tue 19 May 2015:
Thanks guys…
Bryan, I know you’re old school…work the problem until it’s
corrected and NO work arounds. While I myself am also a disciple
of that line of thought, this bulb failure module is just…EVIL!
Pete, so you’re saying that the default ‘‘fault’’ condition is open
circuit on the pink/gray wire. Why then didn’t I get a light when
I cut the pink/gray wire coming out of the rear module?
So if I decide to remove the instrument cluster and track down that
single pink/gray wire going into the VCM I should know if the bulb
light is triggered by a power or no power condition on the wire
simple by cutting it! (But I think I essentially did that by
cutting the rear module�s wire?)–
Groove, 1989 XJ6 3.6L
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In reply to a message from Grooveman sent Tue 19 May 2015:
The wiring diagram shows all 4 modules wired into the one
pin in parallel, so cutting a wire isn’t going to make a
difference. Cut all 4 and the VCM will see zero volts,
which is a fault condition with zero volts presented to the
VCM at pin 32 in the connector. If any of the connected
modules sees a bad bulb, it will take the gray/pink wire to
ground and the VCM reports a bulb failure. I think the best
work-around will be to disconnect the gray/pink wire going
into the 36-pin black connector just behind the driver’s
knee bolster near the ignition key and feed it 12 volts from
a source nearby, say the pink/white wire at pin 12 in the
same connector.–
The original message included these comments:
Pete, so you’re saying that the default ‘‘fault’’ condition is open
circuit on the pink/gray wire. Why then didn’t I get a light when
I cut the pink/gray wire coming out of the rear module?
So if I decide to remove the instrument cluster and track down that
single pink/gray wire going into the VCM I should know if the bulb
light is triggered by a power or no power condition on the wire
simple by cutting it! (But I think I essentially did that by
cutting the rear module�s wire?)
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In reply to a message from Grooveman sent Tue 19 May 2015:
Somewhere in my piles of paper information from 30 years ago
I have the drawing I made for the elimination of the bulb
fail warning on the early (1988/89) XJ40 3.6.
You need to cut and ground a wire (pink/slate I THINK!!!)
not at each module but at the harness near steering column.
The wire goes to the INST PK. You cut the wire and earth it
on the INST PK side.
I have not done this ‘workaround’ in over 2 decades and I
don’t remember where the paper drawing is. I do have it in a
file somewhere but maybe some remembers the procedure.
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In reply to a message from motorcarman sent Wed 20 May 2015:
Alrighty then…
I have both Pete and Bob cutting the single pink/gray(slate) wire
up near the steering column (prior to entering the instrument
pack). But Pete wants to supple the wire going into the pack with
12 volts and Bob wants to ground it.
I guess we’re all in agreement that the single pink/gray wire is
what’s telling the VCM there’s a fault. But just how it’s doing
that seems to be the question.–
Groove, 1989 XJ6 3.6L
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In reply to a message from motorcarman sent Wed 20 May 2015:
There are 2 wires involved in this modification.
The side of the block connector with the SINGLE pink/slate
wire (#32) is CUT and taped back. The other side of the
block connector has two pink/slate wires.
The YELLOW wire (#8) on the side of the block connector with
the TWO pink/slate wires (Opposite side of the connector
where you just cut the pink/slate) gets cut and GROUNDED.
The yellow wire that is earthed is on the connector side
(not the harness side). Leave a few inches of wire leaving
the connector to have enough slack to do this.
I usually crimped a ‘ring’ terminal and earthed it to the
column.
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In reply to a message from motorcarman sent Wed 20 May 2015:
Gentleman…
NOW this is all starting to make sense!
Pete was nice enough to send me a wonderful wiring diagram of the
electrical system. Much Mo better the the one in the Haynes manual.
Bob dusted off a two decades old drawing that he had made of a work
around and kindly forwarded it to me. Luckily he made this drawing
minutes before he passed out when he heard that O. J. was found
innocent!
So it seems that the VCM receives two (count-um 2) inputs from the
four bulb failure modules.
The first input is our friend the pink/gray wire that is triggered
by a ‘‘general’’ bulb failure.
The second input is from a yellow wire that is triggered by a �turn
signals/hazard� bulb failure.
This make sense because with everything intact when I removed
either the reverse bulb or the tail light bulb at the left rear
(the two top bulbs) I would get a warning light as would be
expected. When I then cut the pink/gray wire at the rear left
module and removed either of those bulbs…no light. But with the
wire still cut removing either of the two �turn signals/hazard�
bulbs I would get a light because it appears those bulbs are
monitored separately by the yellow wire.
So what I make of this is that the condition of the front and rear
turn signal bulbs (which are the only bulbs that blink in the
hazard mode by the way) are reported to the VCM through the yellow
wire. All the other monitored bulbs are considered �general� and
their condition uses the pink/gray (or K/S, Jaguars wire color code
for pink/gray or slate) wire.
The elegant solution to the erroneous VCM warning appears to be the
fix that Bob just posted.–
Groove, 1989 XJ6 3.6L
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In reply to a message from Grooveman sent Wed 20 May 2015:
I performed this ‘mod’ on many cars back in the '90s. I did
not even need the drawing after I got used to ‘cutting and
grounding’ but I kept the drawing because I knew I would
forget how to do it if too much time passed. (I was correct!!!)
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In reply to a message from motorcarman sent Wed 20 May 2015:
I am a little confused with some of the information on
these posts as it appears that the slate/pink wire
which ‘feeds’ to the display alarm needs to be grounded if
it is cut ?
On mine I inserted small switches in line on each BFM
pink/slate wires which allows me to ‘cut’ the feed from any
BFM at any time - I use them to trace which corner of the
car is giving me the bulb fail signal - if I put the switch
to off (effectively cutting the wire’ then the fail signal
will disappear once the BFM which is giving the signal is
selected.
This works - so on mine at least I don’t have to ground the
wire to lose the signal
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In reply to a message from Nigel Snowden sent Thu 21 May 2015:
Nigel…
If the system operates like I now think it does your ‘‘switches’’
on the pink/gray wires did in fact disable the ‘‘general’’ monitored
lights from triggering a fault message.
However it would not disable a signal from the ‘‘directional/hazard’’
lights (these being the two lower bulbs in each rear light assembly
and the two rectangular lights below the headlghts). These appear
to be monitored separately by the bulb failure modules ending in
the yellow wire going into the VCM.
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