[xj40] Headlight main / high beam problem

Bryan_N · March 29, 2012, 2:27pm

On my '91 with ‘block’ headlights I discovered that the left
main/high beam is not illuminating - all other lights front
and back working normally and therefore NO BFM warning on
the dash (sorry Dennis!!) because it does not monitor the
headlight main beams.

Started to check :-

Bulb? - looked OK and continuity check main filament good
Fuse? - B8 in left fuse box good
12 V to one side of fuse? - Yes
12 V on Brown/orange wire at BFM board? - No!
12 V out of back of fuse B8? - Yes.
12 V on pin 7 of Black connector LS29 at BFM? - No.
[However a couple of times I saw something around 5 volts at
that pin so I checked pin 8 which gets battery voltage from
a different fuse on a Brown/pink wire for the dipped/low
beam and fog lamp and that was at 12.7 Volts]
Detached left fuse box and unplugged the Black connector
LS72 which carries the Brown/orange wire on pin 3 - as far
as I can see uninterrupted all the way forward along the top
of the left inner wing to the BFM Black connector pin 7.
Checked continuity pin 3 of LS72 to pin 7 of LS29 - NONE!

I can only therefore assume that somewhere in that thick
loom the Brown/orange wire is corroded/broken.

To prove that the rest of the system especially the BFM
(Dennis) is good, I reconnected everything and ran a wire
from the battery positive terminal which I touched on to the
BFM circuit board at the point where the Brown/orange wire
terminates and, with the headlights switched on and main
beam selected, the little relay energised and the LH main
beam filament illuminated like a good’un.

If my analysis is correct and there is a break somewhere
along the length of that Brown/orange wire (which I assume
will be hard to locate) I do not fancy going to the trouble
of re-wiring from the back of the fuse box all the way to
the BFM connector. My initial thoughts are that I will run a
wire from the battery positive terminal via an in-line fuse
and splice it in to the Brown/orange at the BFM to get
battery power to the board to power that left main beam.

I will of course have to leave fuse B8 in place otherwise I
get the dreaded fuse fail warning on the dash!

Anyone have any alternative thoughts on the matter?–
Bryan N, '91 Sovereign 4.0 L, RHD
Cambridgeshire, United Kingdom
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Grooveman · March 29, 2012, 4:24pm

In reply to a message from Bryan N sent Thu 29 Mar 2012:

Bryan…

After reading (and rereading) the very logicsl troubleshooting
steps you took in tracking down your headlamp problem I would be
inclined to agree with your deduction.

…However…

Since I’m not sure how far ‘‘upstream’’ in the BFM you jumped the
live wire from the battery (and if the full battery voltage made a
difference)I would swap the front BFM’s to see what happens. If
nothing changes then you know your problem is happening before it
reaches the BFM. In that case (since you’ve eliminated the fuse) a
broken/shorted wire is almost assuredly your culprit.

If though, the left headlamp works after the swap then you know
it’s your good buddy, the $#&% bulb failure module, and DON’'T COME
CRYING TO ME !!!–
Groove
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Bryan_N · March 29, 2012, 5:27pm

In reply to a message from Grooveman sent Thu 29 Mar 2012:

Dennis,

Let me be a little more explicit.

I found no voltage (or continuity) on the wiring from the
connector at the back of the fuse box right up to the
circuit board on the BFM. (Nor between the BFM connector on
the car harness and the connector at the back of the fuse box.

I have good continuity between pin 7 on the BFM side of its
connector and the circuit board where the Brown/orange wire
which puts (or should put) 12 volts on to the board to both
energise the main beam relay and power the main beam
filament is terminated in a solder joint (which looks good,
BTW).

So in my little experiment, I by-passed the entire circuit
from the battery via fuse B8 through to the BFM connector by
feeding 12 volts directly on to the BFM circuit board at the
point where the Brown/orange wire normally feeds in its 12
volts.

That illuminated the main beam filament when ‘high’ beam was
selected which, I think, demonstrates that the BFM is doing
its job, as of course, they usually do!

I had considered swapping the front BFMs, but concluded that
there was no point in doing so. If you don’t put voltage on
to the BFM, any BFM, it ain’t gonna work.–
The original message included these comments:

After reading (and rereading) the very logicsl troubleshooting
steps you took in tracking down your headlamp problem I would be
inclined to agree with your deduction.
…However…
Since I’m not sure how far ‘‘upstream’’ in the BFM you jumped the
live wire from the battery (and if the full battery voltage made a
difference)I would swap the front BFM’s to see what happens. If
nothing changes then you know your problem is happening before it
reaches the BFM. In that case (since you’ve eliminated the fuse) a

–
Bryan N, '91 Sovereign 4.0 L, RHD
Cambridgeshire, United Kingdom
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Grooveman · March 30, 2012, 2:34am

In reply to a message from Bryan N sent Thu 29 Mar 2012:

Bryan…

Since you have a good operating system on the right headlamp I
imagine you can just read out all the voltages and resistances
on the power feed into the right BFM and compare them to the left.

Obviously if the left BFM is not recieving power then the problem
lies upstream. But for just a few minutes of work why not swap the
BFM’s JUST to be sure. Then you’ve eliminated any doubt.

Of course I can’t envision ANY scenario where a BFM would
malfuntion…Ha ha…Oh yea…Oh man…ha ha…Wait Wait,
I’m not done…Woo woo…that felt really good!–
Groove
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Bryan_N · March 30, 2012, 7:04am

In reply to a message from Grooveman sent Thu 29 Mar 2012:

Dennis,

Unfortunately, on a UK car with ‘block’ headlamps it is not
‘‘just a few minutes of work’’ to remove the front BFMs!

To get at the left bulb holder without ripping the skin off
the back of one’s hand the air filter housing and the
4-relay bracket on the radiator support need to be removed.
That also then allows the BFM and its accompanying harness
to be lifted out - except that it is impossible to get at to
disconnect the two PM4 connectors and the earth-lead bolt
without removing the headlamp unit - and that cannot be
removed without removing the chrome radiator surround!!!

If for one moment I thought that the left BFM was at fault I
would switch it with the right BFM but if the left lights
work as they should when I put the missing 12 volts directly
on to the main beam input from the Brown/orange wire on the
left BFM circuit board I cannot see there being a problem
within the BFM. However, I will try my little experiment
again having ‘slept on the problem’ just to make sure I
wasn’t kidding myself that I had identified the cause yesterday.

That will have to wait though - I have now been ordered to
‘tidy up’ the garden before guests arrive next week! :-(–
The original message included these comments:

Obviously if the left BFM is not recieving power then the problem
lies upstream. But for just a few minutes of work why not swap the
BFM’s JUST to be sure. Then you’ve eliminated any doubt.

–
Bryan N, '91 Sovereign 4.0 L, RHD
Cambridgeshire, United Kingdom
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Nigel_Snowden · March 30, 2012, 9:53am

In reply to a message from Bryan N sent Fri 30 Mar 2012:

Bryan

You say cannot remove headlight without removing the chrome
radiator surround ? - mine can so must have changed - when I want
work on anything there I always remove the headlight unit - only
four nuts and it comes away very easy - takes about five mins max
and makes access to the wiring/BFM so much easier - 13mm spanner

Nigel–
1987 XJ40 3.6 Auto Sov SAJJHALH3AA512874
Singapore, Singapore
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Bryan_N · March 30, 2012, 11:07am

In reply to a message from Nigel Snowden sent Fri 30 Mar 2012:

Nigel,

On my ‘91, the chrome backing for the headlight protrudes
about 1’’ inboard and is trapped by the chrome radiator
surround - only by about �’’ but enough to prevent the unit
being withdrawn forward. The headlight unit is a very snug
fit and has to be withdrawn at exactly the correct angle to
avoid the fixing studs binding on the slots in the body.
Care is also needed to avoid tearing the headlamp unit seal
which tends to ‘bond’ itself to the body but that is
probably because the unit has not been out in the last 16
years - never having had a front BFM problem of course in my
ownership. [For Dennis’s benefit! :-)]

BTW, didn’t you have a corroded wire problem in the lighting
loom some years ago?–
The original message included these comments:

You say cannot remove headlight without removing the chrome
radiator surround ? - mine can so must have changed - when I want
work on anything there I always remove the headlight unit - only
four nuts and it comes away very easy - takes about five mins max
and makes access to the wiring/BFM so much easier - 13mm spanner

–
Bryan N, '91 Sovereign 4.0 L, RHD
Cambridgeshire, United Kingdom
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Bryan_N · March 30, 2012, 3:48pm

In reply to a message from Bryan N sent Fri 30 Mar 2012:

GOT IT!!!

Having finished my gardening chores early (how I hate that
job!) I tried my little experiment again - putting 12 volts
directly on to the BFM circuit board to demonstrate that the
system worked but was not otherwise getting voltage from the
fuse box on the Brown/orange wire to power the main beam.

Worked like a charm again so once more I investigated that
Brown/orange wire. This time I saw 7 volts momentarily at
the BFM so I concluded that there was corrosion in the wire
between it and the fuse box which was giving a high
resistance feed occasionally - but not enough volts to
energise the relay to illuminate the main beam filament.

I started to closely inspect the Brown/orange wire working
back from the BFM as it disappeared in to the large main
loom and EUREKA! there is was - a nice green oxide of copper
bursting through the insulation right where the wire was
kinked to enter the main loom behind the left headlamp.

I will post a couple of pictures to illustrate the problem.

I have unwound the taped loom a few inches either side and
cut out a couple of inches of the wire where the copper
conductor is nice and clean and will tomorrow splice in a
piece of wire to join it all up again (Would have done that
today but I can’t find my box of heat-shrink sleeving to put
over the soldered joints)

Meanwhile I checked continuity upstream and downstream of
the cut wire and all is good so I hope that will be the
final fix.–
The original message included these comments:

If for one moment I thought that the left BFM was at fault I
would switch it with the right BFM but if the left lights
work as they should when I put the missing 12 volts directly
on to the main beam input from the Brown/orange wire on the
left BFM circuit board I cannot see there being a problem
within the BFM. However, I will try my little experiment
again having ‘slept on the problem’ just to make sure I
wasn’t kidding myself that I had identified the cause yesterday.

–
Bryan N, '91 Sovereign 4.0 L, RHD
Cambridgeshire, United Kingdom
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Grooveman · March 31, 2012, 2:08am

In reply to a message from Bryan N sent Fri 30 Mar 2012:

Bryan…

GOOD MAN !! Your deductive powers are an inspiration to us all.

I’d still smack the BFM with a large spanner though.–
Groove
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Nigel_Snowden · March 31, 2012, 12:00pm

In reply to a message from Bryan N sent Fri 30 Mar 2012:

Bryan

OK they must have changed things a little between yrs and mine - my
chrome front only engages with teh hrome light surround by about 3
or 4 mm so it quite and ewasy wiggle to get them out.

Yes I had a problem there, was caused by the wiring loom ‘cooking’
hard, once there was a crack on the sheathing then wire was exposed
and also 'cooked’and coroded so that when I moved the harness one
broke

Constant problem out here where usual temperature is 30C all year
round.

Nigel–
1987 XJ40 3.6 Auto Sov SAJJHALH3AA512874
Singapore, Singapore
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Bryan_N · March 31, 2012, 12:31pm

In reply to a message from Grooveman sent Fri 30 Mar 2012:

LOL!

Job done.

Soldered a splice connecting the good parts of the
Brown/orange wire and covered the joints with heat-shrink
sleeve. Everything back to normal and all lights working
again without the need to physically abuse the BFM!

I see that the photographs of the corroded wire now appear
in the album:-

http://www.jag-lovers.org/snaps/snap_view.php3?id=1333131431--
The original message included these comments:

GOOD MAN !! Your deductive powers are an inspiration to us all.
I’d still smack the BFM with a large spanner though.

–
Bryan N, '91 Sovereign 4.0 L, RHD
Cambridgeshire, United Kingdom
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–
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Grooveman · April 1, 2012, 6:33am

In reply to a message from Bryan N sent Sat 31 Mar 2012:

Bryan…

Excellent job of Sherlock Holmesing. Glad you solved your problem!

Now in The good old US of A we would say ‘‘that wire was really
screwed up’’. But I imagine you UK blokes would pontificate that
‘‘that was a right nasty biy of kit’’

Please though (even though it wasn’t at fault), just for me, smack
that BFM just once!

Is LOL ‘‘lots of luck’’ or ‘‘Laugh out loud’’…Sorry I just arrived
on the turnip truck this very morning.–
Groove
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Bryan_N · April 1, 2012, 7:09am

In reply to a message from Grooveman sent Sat 31 Mar 2012:

Dennis,

I did mention in an earlier post that when I discovered that
corroded wire I exclaimed ‘‘Eureka!’’. That is not strictly
true. What I actually said out loud was ‘‘you little
ba*tard!’’ - which was unfortunate since my wife at that
precise moment had just entered the garage…

I had to explain that was a technical term widely used in
motor wrenching circles to explain why 12 volts wasn’t
getting from A to B to light the lights. She readily
accepted that - with the admonition that ‘‘It had better be
OK when we use the car over the holidays’’.

No soul, these ladies!

Just to please you, I will give that front BFM a love tap
and tell it that it is from Dennis.–
The original message included these comments:

Now in The good old US of A we would say ‘‘that wire was really
screwed up’’. But I imagine you UK blokes would pontificate that
‘‘that was a right nasty biy of kit’’
Please though (even though it wasn’t at fault), just for me, smack
that BFM just once!

–
Bryan N, '91 Sovereign 4.0 L, RHD
Cambridgeshire, United Kingdom
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