Have got my new XJ40 acquisition to a roadworthy state but
they pinged me on the bulb failure signal despite my
demonstration that all the signals worked.
Is it possible to trick this unit? I have followed a number
of posts and swapped the rear units over and the fault
followed so I’m pretty confident It’s the unit.
I’ve pulled the unit apart to get at the PCB (as I have a
short time limit for the roadworthy process).
I note there are 6 relays on the board. Before I go out and
stuff around with the open board in place I was actually
wondering if I could either shove a bit of cardboard in
each relay contact to either keep them open / or closed (I
don’t know their happy state)
I note it’s possible to re solder for possible dry joints
(but I’m a mech eng not an elec, and my solder iron is a
touch on the brutal side)
I’ve got a second hand unit on it’s way but the tyranny of
Australia Post against my location will see me default on
the roadworthy process and cost me money I don’t wish to
waste.
Any one know any dodgy that will last a 5 second
demonstration?–
MKE
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In reply to a message from MKE sent Sun 12 Oct 2014:
One of the wires from each of BFM is pink / slate
If you cut this one then the alarm will stop - for mine I
have actually inserted a small switch on each BFM which
allows me to isolate which one is causing the alarm when I
do get it.
I just turn the switch off at each unit until the alarm
stops and then at least I know which unit the fault is at.
I kept getting the alarm without any bulbs appearing to
have failed so thats why I did this.
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In reply to a message from MKE sent Sun 12 Oct 2014:
This is on an '88 XJ40, yes? (best to state that whenever
you post a question)
I don’t recognise the 4-pin and 18-pin connectors to which
you refer
According to the circuit diagrams for an '88 model, the
Pink/slate wire goes to:-
Front BFMs - the 9-way yellow connector pin 8
Rear BFMs - the 15-way black connector pin 6
The adjacent pins to those with the Pink/slate wire at each
connector are wired thus:-
Right front.
pin 7 = Pink/green
pin 8 = Pink/slate
pin 9 = Pink/blue
Left front.
pin 7 = Pink/red
pin 8 = Pink/slate
pin 9 = Pink/yellow
Right rear.
pin 5 = Yellow/pink
pin 6 = Pink/slate
pin 7 = Pink/green
Left rear.
pin 5 = Yellow/slate
pin 6 = Pink/slate
pin 7 = Pink/red–
The original message included these comments:
I have no pink/slate.
I have the unit in front of me.
Large round four pin connector.
18 Pin Connector
Lots of colours, but couldn’t find a pink / Slate among them
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In reply to a message from Bryan N sent Sun 12 Oct 2014:
Yeah, 88 XJ40.
I got the wife to check my colour blindness and she did
indeed point out a pink and very lightly slate stripe wire.
Cut it/ re installed but still alarming.
It’s a bit dark and late out now so I’ll have another look
tomorrow.
I’m a bit confused that the right and left rear’s are
different pin combo’s, as I have swapped left to right so
I’ll look at that as well. ( the indicator cycle time
indicator followed it)
But I definitely have
A large round four pin wired to the BFM,
A small round two pin. (and a separate earth wire.)
And then a medium multi pin (with three pink wires within
the cores.)
One clearly Pink/Blue stripe.
One apparently pink/slate stripe (so my wife tells me but I
can’t see it.)
And another pink ( again I can’t see a stripe)
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In reply to a message from MKE sent Sun 12 Oct 2014:
Mike,
I can’t explain why you are seeing different connectors to the
ones shown in the circuit diagrams - but it is an early Jaguar
so I guess it may be possible.
Why are you concentrating on the rear BFMs only? A failure
could be detected (or caused) by any of the four BFMs.
You mention ‘‘the indicator cycle time’’. What do you mean by
that?
Presumably you are aware that a BFM warning can be caused by a
bad connection or solder joint resulting in a high resistance
which is what the BFM is measuring before deciding to give a
warning and that high resistance may not prevent the actual
light involved from illuminating.
I assume that your car has the indicator side repeater lamps
on the side of the front wing? I had all sorts of problems
with those on my car caused by corrosion in the bulb socket
the high resistance from which triggered a BFM warning without
having any effect on the operation of the indicators
themselves but it did alter the dash indicator ‘blink’ speed.
Worth checking?–
The original message included these comments:
I’ll look at that as well. ( the indicator cycle time
indicator followed it)
But I definitely have
A large round four pin wired to the BFM,
A small round two pin. (and a separate earth wire.)
And then a medium multi pin (with three pink wires within
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In reply to a message from MKE sent Sun 12 Oct 2014:
Mike
Thast right there are three multi wire connectors - you
need the big one with many wires .
Mine is one of the earliest 3.6 so yours should be the same
ALL the BFM have the pink/slate wire there and it does need
good light to see the slate, especially on the older ones -
you may need to peel back a little of the insulation to see
the colours more clearly.
Best bet would be to cut the pink / slate wire from every
BFM as I suspect you don’t actually know which one is
causing the alarm at this stage - that’s why I cut them all
and put in the switches.
The BFM are VERY sensitive to voltages which don’t meet
their parameters
Best luck but it DOES work - once you find the wire then it
will stop the alarm - they all common up at the junction to
the dashpack (#32 wire on the black 36 wires junction to
the dashpack so you can actually disable all by cutting one
wire !)
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In reply to a message from Nigel Snowden sent Sun 12 Oct 2014:
Nigel,
There may be one small(?) downside to cutting those BFM
wires as you suggest IF in doing so you do not see the
bulb-fail icon on the dash during the initial light check
sequence when you first turn on the ignition. Is that
inhibited too?
I know that the UK MoT people would fail a car which does
not show a warning icon during the light check phase.–
The original message included these comments:
Best luck but it DOES work - once you find the wire then it
will stop the alarm - they all common up at the junction to
the dashpack (#32 wire on the black 36 wires junction to
the dashpack so you can actually disable all by cutting one
wire !)
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In reply to a message from MKE sent Sun 12 Oct 2014:
Hi, I appreciate your tight time window, and I realise the
bfm controls are regular culprits, but I think before you
start cutting wires you want to be certain it’s not just a
case of high resistance triggering the warning light.
As Bryan has mentioned, the wing repeaters are very
suspect, on my old Sovereign I actually found grass growing
in mine despite it working fine ! and once I’d cleaned the
contacts the bfm light went out. Another time I cured the
warning light by changing a rear light bulb, I swapped a
blown bulb and the replacement which was identical lit up
fine but the warning light was still coming on, I tried
another bulb and the warning light disappeared. Out of
curiosity I tried the first bulb in the opposite side and it
triggered the bfm light again.
The No. plate lamp bulb holders can also corrode and still
look bright enough to pass a vehicle test, my own fell apart
when I attempted to change a bulb.
I’m just thinking that checking the above first won’t take
too long, and even giving each bulb a little twist in it’s
holder has been known to work.
good luck.–
The original message included these comments:
they pinged me on the bulb failure signal despite my
demonstration that all the signals worked.
of posts and swapped the rear units over and the fault
followed so I’m pretty confident It’s the unit.
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In reply to a message from Casso sent Sun 12 Oct 2014:
Mike,
In addition to Casso’s mention of the number-plate lights
(there are two bulbs and both need to be working) other
favourites which are often missed are the rear brake lights,
the reversing lights and the front fog lights - or the
ballast resistor in the fog light connectors under the front
bumper which have to be present if front fogs are not fitted
to fool the BFM in to thinking they are.
All are worth investigating before you start cutting wires.–
The original message included these comments:
The No. plate lamp bulb holders can also corrode and still
look bright enough to pass a vehicle test, my own fell apart
when I attempted to change a bulb.
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In reply to a message from Bryan N sent Sun 12 Oct 2014:
I followed some advice after searching the forums.
One suggestion was to swap the L rear to the R rear as
confirmation it was indeed the BFM. I did this and the dash
indicator blink speed( what I called the indicator cycle
time)followed the transferred unit. I understood this to be
a confirmation that it was a rear BFM failure.
I checked the side indicators (I think you had suggested in
a previous post (not my first attempt at sorting this out
but I’d given up thinking physical confirmation of all
bulbs working would pass the roadworthy) In fact I have
pulled every globe and socket just to check)–
MKE
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In reply to a message from MKE sent Sun 12 Oct 2014:
Mike,
That’s the first time I’ve heard of that. My understanding
was that the rear pair of BFMs are fully interchangeable
left and right (as are the front pair of BFMs) and so
switching sides should make no difference to their function unless there is a fault in one of them in which case that
fault will travel across the car with its BFM.
Are you saying that, for example, with the left indicator
selected, the dash repeater blink speed is faster or slower
than the actual left indicator’s blink speed, suggesting a
fault in the left front and/or rear (or side wing repeater)
indicator circuit but when you select right indicator that
fault is not present? Further, when you switch the rear BFMs
left to right and vice-versa that dash repeater blink speed
fault now appears when the right indicator is selected but
not when the left indicator is selected?–
The original message included these comments:
One suggestion was to swap the L rear to the R rear as
confirmation it was indeed the BFM. I did this and the dash
indicator blink speed( what I called the indicator cycle
time)followed the transferred unit. I understood this to be
a confirmation that it was a rear BFM failure.
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In reply to a message from Bryan N sent Sun 12 Oct 2014:
Bryan
Yes there may be a downside however - the flash of the bulb
failure on ignition on with mine does not actually happen
(or its so fast that I never see it !!)
I am not sure about that sequence but assume that check MAY
be ECU generated rather than BFM generated.?
On mine I recently had the BFM on/off intermittently for
some weeks and tried to trace it (it was the left front
unit which I knew because of my switches !)
Tried and checked everything and it was only by chance that
I noticed that one of the wires into one of the multiplugs
was about to break right at the junction where it entered
the plug - on checking found three others were in the same
condition on that multi plug alone (ie all of them !) !! -
and two actually broke whilst I was ‘jiggling’ the plug !
Checked all the multi plugs at the front left and right and
found another two on the right which were about to part.
Car now 27 years old and the wires on several of the wire
looms have now ‘cooked’ hard - any movement makes them
susceptible to breaking
The multiplugs with the inbuilt resistor which fools the
BFM into thinking that there are some front fog lights is
very likely to corrode at its soldered connection.
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In reply to a message from Nigel Snowden sent Sun 12 Oct 2014:
Nigel,
I wonder if the ‘ignition on, dash light check phase’ is
different on the earlier ‘digital dash’ cars then? On my
'91, (with the analogue dash) when the ignition was first
turned on (before engaging the starter), all of the dash
warning icons illuminated and stayed on for about 5 seconds.
That is the first thing that my local MoT tester checked
when he got in to the car. IIRC, if any of the safety
significant warning lights (e.g Lights, Brake, ABS) did not
appear, he wouldn’t pass the car in the same way that he
wouldn’t pass the car if they were illuminated after he
started the engine.
Your comment about the deterioration in wiring with age
reminded me of a problem I reported a couple of years ago
which you may remember. Re-reading that thread brought back
some happy memories!
I suppose Mike could have a similar wiring problem on his
car - very difficult to identify and locate.–
The original message included these comments:
Yes there may be a downside however - the flash of the bulb
failure on ignition on with mine does not actually happen
(or its so fast that I never see it !!)
Car now 27 years old and the wires on several of the wire
looms have now ‘cooked’ hard - any movement makes them
susceptible to breaking
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In reply to a message from MKE sent Sun 12 Oct 2014:
Alright I just read the 14 posts on this subject and I have only
one question…
What can I do to keep from EVER getting BFM warnings on my '89’s
VCM…Whatever it is, I’LL DO IT!! I believe I’ve mentioned in the
past that I hate that *&$! system and feel personally persecuted by
it.
As far as a vehicle inspection here in Texas, on a car 25 years or
older. brakes, horn, lights, and wipers. and you’re go to go
another year on our highways at 85mph (you’ve got to love this
place!).–
Groove, 1989 XJ6 3.6L
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In reply to a message from Grooveman sent Mon 13 Oct 2014:
85mph - ah yes I can still remember such speeds in the
distant past! Lucky Texans!
OTOH, here on Vancouver Island, vehicle testing is but a
distant as memory as 85mph!!
I think we got rid of all testing here about 20 years ago
and in ever-so-green Vancouver City, emissions testing is to
be abandoned in January - so no testing at all for pleasure
vehicles in BC after that.
Mine is not to reason why btw
Larry–
The original message included these comments:
As far as a vehicle inspection here in Texas, on a car 25 years or
older. brakes, horn, lights, and wipers. and you’re go to go
another year on our highways at 85mph (you’ve got to love this
place!).
Groove, 1989 XJ6 3.6L
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In reply to a message from abercanadian sent Mon 13 Oct 2014:
Thanks everyone.
I’ve been away for work for a couple of days so I’ve missed
a few posts.
After trying cutting the pink/slate wire, and getting no
result, and given I was running out of time I ordered a
good replacement BFM. (Price a very reasonable $45 Aus.)
and delivered the next day.
Installed and all fixed.
So tally so far was
fixing the brake low light (New pads)
Fixing the ABS fault (Resoldered the dry joints on the ABS
power feed relay)
And finally replacing the faulty BFM unit. I’ll re solder
the old one and see if I get it live again.
NO dash faults : I should be registered this afternoon.
Thanks everyone.
We won’t talk about having to replace the ignition key
assembly - that one took me half the night undoing the
security bolts with a pin punch and a hammer and then
finding out if you press the tab and key position two it
neatly slides out. Oh well.–
MKE
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In reply to a message from MKE sent Tue 14 Oct 2014:
I was going to chime in and say that in my opinion trying
to cheat the bulb failure warning system is a highly
dangerous and ill-advised procedure and I am surprised that
so many enthusiasts even talk of it! I just hope I don’t
meet any of them on the highway coming the other way.
I suffered for months from this and the solution was to find the fault. First of course is the unit doing its
job? ie are there failed bulbs. Second, the most likely
fault in the BFM module itself is a dry soldered joint.
Going through them all carefully using a jeweller’s loupe
will eventually find the culprit, which is what I did. Now
I know I have a safety sentinel without the false alarms.–
The original message included these comments:
good replacement BFM. (Price a very reasonable $45 Aus.)
and delivered the next day.
Installed and all fixed.
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In reply to a message from Alan4d sent Wed 15 Oct 2014:
Alan
Very good points however we were I think all trying to
assist in order that the vehicle could at least get through
the test - don’t think anyone actually advised that the
bypassing should be considered as a permanent ‘fix’
My own ‘switches’ are purely there so that I am able to
trace which BFM is giving the signal - as we are aware it
is a frequent occurrence that all the lights work but we
still get the warning so in that case its a bit hit and
miss trying to decide which ‘corner’ of the car is
producing the fault signal.
Once the ‘corner’ has ben identified then its easier to
find the fault rather than chasing all four corners
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