'94 XJ40, 164K miles. I noticed that the left low-beam was not
working, so I bought a bulb. Before pulling the bulb out of the
package, I swappped the left and right bulbs, and either worked in
the right hand position, but neither worked in the left. BFM,
right? So I pulled the cover off the left hand BFM and confirmed
that I could turn the headlamp by pressing the relay contact. By
the way, the fog lamp on the left was not working either, but I
could turn it on by pressing the relay contact directly. So, I
pulled the BFM to look for broken connections or burned spots -
nothing apparent. After pricing replacements online, I decided to
swap left and right BFM’s and see what happened. Well, the left
hand lights still don’t work, and the right hand side ones do.
Since it’s both the headlamp and foglamp involved, I checked the
fuses - I even swapped another 15 amp fuse into the headlamp/
foglamp fuse spot - no change. So… what next? Any of you folks
know where I might look? The Haynes wiring diagram is only
marginally helpful.
RickG
'94 XJ6, 164K miles - Hell’s Belle–
RickG
Federal Way, WA, United States
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In reply to a message from RickG sent Fri 9 Apr 2004:
Rick, I had a similar problem, try squeezing & twisting the multi-
plug connectors,as if theres a bad connection in one of these, that
will do it, also, clean the earth connection too.With my Bfms, they
LOOKED ok, but I re-melted the Solder on all the Pins that connect
to the large Feed Cables too! I did all this in one go, so I m not
sure which cured it, but one of them did! Good Luck, Bernie–
The original message included these comments:
'94 XJ40, 164K miles. I noticed that the left low-beam was not
working, so I bought a bulb. Before pulling the bulb out of the
package, I swappped the left and right bulbs, and either worked in
the right hand position, but neither worked in the left. BFM,
right? So I pulled the cover off the left hand BFM and confirmed
that I could turn the headlamp by pressing the relay contact. By
the way, the fog lamp on the left was not working either, but I
could turn it on by pressing the relay contact directly. So, I
pulled the BFM to look for broken connections or burned spots -
nothing apparent. After pricing replacements online, I decided to
swap left and right BFM’s and see what happened. Well, the left
–
mesh grilled kiwi wheeled xj40Daimler1990
Dover, United Kingdom
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Rick
Check if you are getting volts on the wiring to the BFU from the
lighting logic module. Seeing that the output to the front fogs is
common L & R you should be able to find a fault, maybe in the plugs and
sockets.
NW
RickG wrote:
'94 XJ40, 164K miles. I noticed that the left low-beam was not
working, so I bought a bulb. Before pulling the bulb out of the
package, I swappped the left and right bulbs, and either worked in
the right hand position, but neither worked in the left. BFM,
right? So I pulled the cover off the left hand BFM and confirmed
that I could turn the headlamp by pressing the relay contact. By
the way, the fog lamp on the left was not working either, but I
could turn it on by pressing the relay contact directly. So, I
pulled the BFM to look for broken connections or burned spots -
nothing apparent. After pricing replacements online, I decided to
swap left and right BFM’s and see what happened. Well, the left
hand lights still don’t work, and the right hand side ones do.
Since it’s both the headlamp and foglamp involved, I checked the
fuses - I even swapped another 15 amp fuse into the headlamp/
foglamp fuse spot - no change. So… what next? Any of you folks
know where I might look? The Haynes wiring diagram is only
marginally helpful.
RickG
'94 XJ6, 164K miles - Hell’s Belle
RickG
Federal Way, WA, United States
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In reply to a message from Norman sent Fri 9 Apr 2004:
First, my understanding of the BFM is that the lighting control and
the bulb failure detecion is all in the same little box, mounted
just forward of the air filter on the left side, and in the
corresponding position on the right. On this model, the lighting
control box contains one PC board with relays and various diodes
and other bits soldered to it. There are 4 connectors - 2 big
multi contact plugs and 2 bulb plugs for the headlamps.
In my testing, the lighting control module and its connectors
appear to be OK - The I’ve swapped modules between the left and
right sides and the low beam and fog do not work on the left side
using either module. The right side lamps work fine using either
module.
So the trouble appears to be ‘‘upstream’’ of the lighting control
module. Since fog and low beam are both affected, and both are on
the same fuse circuit, I checked and even replaced the fuse. No
improvement. So I’m looking for a fault in a connector or wiring
between the dash lighting switch and the left-hand lighting control
module. I hoped that there would be some ‘‘common’’ failure point in
the XJ40’s that others had encountered before me. An archives
search only turned up one likely candidate – a loose/failed
connection in the fuse block. That would explain the symptoms, and
it shouldn’t be too difficult to check. I found that lead last
night way past my bedtime, so I guess I’ll check into it this
weekend.–
RickG
Federal Way, WA, United States
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Rick,
I may be out of place with this suggestion but my experience is that
many faults like this are related to corrosion and bad connections with
contacts and bulb sockets. I am a big believer in cleaning electrical
contacts and coating with dielectric grease, its cheap anyone can do it
and solves so many problems I can’t believe it. I have even removed the
plugs on the window solenoids and fuel injectors and cleaned and coated
them.
Jay 90 VDP Majestic
RickG wrote:
In reply to a message from Norman sent Fri 9 Apr 2004:
First, my understanding of the BFM is that the lighting control and
the bulb failure detecion is all in the same little box, mounted
just forward of the air filter on the left side, and in the
corresponding position on the right. On this model, the lighting
control box contains one PC board with relays and various diodes
and other bits soldered to it. There are 4 connectors - 2 big
multi contact plugs and 2 bulb plugs for the headlamps.
In my testing, the lighting control module and its connectors
appear to be OK - The I’ve swapped modules between the left and
right sides and the low beam and fog do not work on the left side
using either module. The right side lamps work fine using either
module.
So the trouble appears to be ‘‘upstream’’ of the lighting control
module. Since fog and low beam are both affected, and both are on
the same fuse circuit, I checked and even replaced the fuse. No
improvement. So I’m looking for a fault in a connector or wiring
between the dash lighting switch and the left-hand lighting control
module. I hoped that there would be some ‘‘common’’ failure point in
the XJ40’s that others had encountered before me. An archives
search only turned up one likely candidate – a loose/failed
connection in the fuse block. That would explain the symptoms, and
it shouldn’t be too difficult to check. I found that lead last
night way past my bedtime, so I guess I’ll check into it this
weekend.
RickG
Federal Way, WA, United States
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I have not followed this thread from its start, but based on your last
posting, you do have an “upstream” common item that affects all lighting.
The lighting relay modules (BFMs by the correct name) are slave devices.
There may be nothing wrong with these devices and you can still have all
kinds of lighting control problems. Having said that, the lighting relay
modules are historically a weak link in the system, especially on early
cars.
The master device for the lighting relay modules and a few other items is
the “Lighting Logic Module”. It provides the control signals for just about
all the vehicle external / instrument panel lighting. This device is
located in the left side instrument pod beside the steering wheel. You need
to drop the bottom panel of the pod (two screws) to remove it.
Absolutely disconnect battery power before attempting this inspection /
replacement! There are “hot” circuits in this device and you will damage
the circuit board it you inadvertently touch a ground while manuvering it
out of the pod. You need to remove the lighting control switch as well.
There is nothing the average (or highly technically inclined) owner can do
with this module other than inspect it for obvious flaws. However, these
modules have been known to exhibit poor quality solder joints … mine was
poorly done. Such a shame too, as a quality solder connection is the best
electrical joint which will last indefinitely … a cold or weak joint is
nothing but trouble. Best course of action, after checking the solder
joints, is to “swap it” with a known good Lighting Logic Module to
operationally test it … assuming no bad joints were discovered with your
original module.
Now the bad news, the Lighting Logic Module is wickedly expensive if
purchased new … $350+. It would be far more cost effective to find a good
used one from one of the usual suspects (parts suppliers). I believe there
are at least three or four models of this device used within the XJ40 model
range. Make sure you locate one that is correct for your Jag. It really
helps to review and study the Electrical Guide for your car when doing this
work.
Good Luck,
John P.
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