[xj40] LED bulbs

It’s been a long time. The great beasty is in the body shop
getting the dings and dimples out and a respray. (original colour,
Morrocco red). While he’s there, I was considering changing out
the bulbs for LED equivalents. Haws anyone here had any
experience with this? and any pros/cons about this change-over?.
Thanks to all who have helped us in the past. MMN–
Matt N.: 93 VDP, 91Peugeot, 02R.Rover
Sandy, OR, United States
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In reply to a message from COPS45 sent Tue 3 May 2016:

Matt,

If you do a search on the XJ40 forum archives for ‘‘LED
BULBS’’ you will find 7 pages of posts on the subject.

Never tried it myself because I feared some complications
with the BFM system.–
The original message included these comments:

It’s been a long time. The great beasty is in the body shop
getting the dings and dimples out and a respray. (original colour,
the bulbs for LED equivalents. Haws anyone here had any
experience with this? and any pros/cons about this change-over?.


Bryan N, now Jag-less, but fun while it lasted.
Cambridgeshire, United Kingdom
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In reply to a message from Bryan N sent Tue 3 May 2016:

Matt…

I have to agree with Bryan (and what Jaguar owner with
even half a brain wouldn’t) that installing LED lights
would almost certainly trigger the infamous BFM warning
light.

So what better reason to hack that finicky system and
never see the dreaded ‘‘bulb failure’’ warning light again!
Even if your new LED lights do trigger the warning you
won’t see it displayed. It’s a win, win…WIN!–
Groove, 1989 XJ6 3.6L
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In reply to a message from Grooveman sent Wed 11 May 2016:

Groove, I nearly always agree with you (and of course
Bryan) but in this instance, and with all due respect…not
so much. At the risk of jinxing myself, the bulb failure
system in my '94 has worked flawlessly. Just this morning
when I got in the old girl to go to work the bulb out
warning light was lit and surely enough, my right tail
light bulb was out. I may not have realized that until
some nice officer of the law stopped me to, um, enighten me
and lighten my wallet. I replaced the bulb with a proper
incandescent bulb but I have been sorely tempted to try
LEDs in lieu of the exterior bulbs after having relamped
(?) my instrument binnacle with LEDs several years ago
(pics in the photo album). And the forum needs a guinea
pig, so…to be continued…–
The original message included these comments:

I have to agree with Bryan (and what Jaguar owner with
even half a brain wouldn’t) that installing LED lights
would almost certainly trigger the infamous BFM warning
light.
So what better reason to hack that finicky system and
never see the dreaded ‘‘bulb failure’’ warning light again!


Mike Stone - 1994 XJ6/XJ40 - 174,XXX miles
Springfield, Missouri, United States
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In reply to a message from Mike Stone sent Wed 11 May 2016:

Mike,

Absolutely! My experience mirrors yours exactly. The BFM on
my car worked perfectly with never a false warning.

I think Dennis suffers from BFphobia - or whatever the
clinical term is for a pathological hatred of Jaguar’s
masterpiece in electrical trickery. :slight_smile:

Dennis - I’m afraid there is no cure other than amputation
of the offending equipment as you have now done.–
The original message included these comments:

Groove, I nearly always agree with you (and of course
Bryan) but in this instance, and with all due respect…not
so much. At the risk of jinxing myself, the bulb failure
system in my '94 has worked flawlessly. Just this morning
when I got in the old girl to go to work the bulb out
warning light was lit and surely enough, my right tail
light bulb was out. I may not have realized that until
some nice officer of the law stopped me to, um, enighten me


Bryan N, now Jag-less, but fun while it lasted.
Cambridgeshire, United Kingdom
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In reply to a message from Bryan N sent Thu 12 May 2016:

BFphobia !!!

Well I am extremely pleased to report that now that my car
has undergone it’s highly successful BFM hack
(’‘Litegonawayomy’’ being the correct medical term for the
procedure) my years of suffering and nervous anticipation
are…totally in remission and hopefully a thing of the
past. A tip of the hat to Dr. Jaguar Pete who assisted in
the operation and stood by me through the darkest of days.

OBVIOUSLY Jaguar cars must have terminated the man who
designed my BFM (I believe his name was Nigel, son of
Lyons) and replaced him with a much more talented module
aficionado to design the one in your car (hmmm I wonder if
he was an American, maybe named Lance or Rock).

Anyway as a result of the Litegonawayomy my driving
experience has been, as Edd China would say … greatly
enhanced.–
Groove, 1989 XJ6 3.6L
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Groove,

My curiosity finally got the better of me and I decided I would get a pair of LED bulbs and experiment. The 1156-type (single filament) bayonet base ‘bulbs’ will fit - now mind you, I’m not saying they are CORRECT - in the reverse light sockets and in the rear ‘guard’ (fog) light sockets on our cars. Tried the LED 1156-types in both places and found that there was no bulb out indicated UNTIL the LED was illuminated (by placing the tranny in reverse in the one case, or switching on the rear guard/fog lights in the other case) at which time the glowing ‘bomb’ appeared on the warning light panel. Curious, eh? A little research and I learned that the resistance through the filament in an incandescent light changes (increases) when the light is illuminated. Who’da thunk? So I guess our BFMs are blessed with some measure of ‘intelligence’ - they detect that a bulb (LED in this case) is present so no worry. However, when that lighting circuit is energized the BFM detects that the resistance is not what it should be (the LED’s resistance is much less than an incandescent) and throws up a warning. Makes sense, I suppose, given that vendors provide a separate resistor module for use with LEDs that are installed as turn signal bulbs. Sans the resistor module the old-school flasher modules freak out and the turn signals flash rapidly (hyper-flash, as they say). So, I suppose some type of resistor could be added to our cars’ light circuitry to fool the BFMs into thinking all is well when LEDs are lit. One of my concerns with doing that is the BFM may then be unable to detect a true lights-out condition. And I - like Bryan N. - have found the BFMs to work as designed and to provide a valuable function, so I’d hate to screw that up. Doesn’t mean I’ve given up on figuring a way to use LEDs in the exterior lighting of our cars, only that more study and/or experimentation is needed.

i fitted canbus corrected led bulbs and no warning lights on the dash

I tried a pair of CANbus LEDs as taillights. No bulb failure warnings but after 20 min. of operation the both went dark. i suspect overheating caused it because after being switched off for several hours they illuminated again, but not wanting to risk a dark hind end I pulled them and put the incadescent bulbs back in. I haven’t experimented with them since.

Thats very strange i have them in my number plate lights, tail lights and fog lights never had an issue, indicators have led bulbs with resisters fitted

I presume we’re talking rear fogs here Phil?

And front driving lights just main and dip not changed

What year is your car Phil? - do you have the built-in the spoiler fogs? (the ones that melt with OEM bulbs)

93/94 With the built in fogs, With leds in no more molten lights have plain leds in with 50 amp resistors to put warning lights out on dash far better light

Interesting! might give it a shot …I’m afraid to turn mine on for more than 20 secs!

if you put resisters in it allows you to run plain led bulbs and keeps the warning lights off on the dash + points brighter lights ,no heat so no brittle lights