[xj-s] change running lights to LED's

Is there any problem with the dash diagnostic for a light or lights out with the LED replacements for running lights?

Thanks, Paul–
Ptipon
Sonora/CA, 90 XJS-V12 conv, United States
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In reply to a message from Ptipon sent Mon 30 Nov 2009:

I believe there will be a problem because the LED’s don’t have
enough current flow to properly activate the bulb failure units.
That could probably be remedied by using some bypass resistors in
parallel with the LED’s. Seems to me someone went through this
exercise before. Do a search of the archives–
lockheed
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lockheed wrote:

I believe there will be a problem because the LED’s don’t have
enough current flow to properly activate the bulb failure units.

That’s correct; you will be rewarded with the bulb failure indicator
being on all the time. Of course, LED units rarely burn out, so you
could arguably just remove the bulb failure units from the circuit.

That
could probably be remedied by using some bypass resistors in parallel
with the LED’s.

That whole idea is just laughable. You can buy resistors made just
for this, but when you see how much they want for them you’ll gag.
So, the most plausible thing to use for a resistor is – a light
bulb. Just take the light bulb you removed from the socket and wire
it back into the circuit somewhere else and hide it so the light
doesn’t bother anyone. Of course, you’ll have to replace it whenever
it burns out. And, perhaps worth noting: No matter what you use for
a resistor, the only thing the bulb failure sensor will be doing for
you is telling you when your resistor has gone bad; it WON’T tell you
when the LED’s aren’t working.

Might as well just remove the bulb failure sensors.

– Kirbert

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In reply to a message from Kirbert sent Tue 1 Dec 2009:

Or, keep the incandescent bulbs.

A whole lot easier and cheaper both in money and labor.

Noel–
'92 XJS Conv, '88 XJS, 68 XKE, 1914 &'15 Ford Model T’s
Edmond, OK, United States
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In reply to a message from Kirbert sent Tue 1 Dec 2009:

Don’t know exactly which expensive ‘‘made for this’’ resistors
you mean Kirby, and would like to know.

I put LEDs in a BMW and installed in parallel common cheap
resistors. Don’t remember exactly, but something around 35
Ohm, which was what gave the same current as the removed
bulb. Yet it didn’t fool the on-board computer which kept on
displaying ‘‘burnt bulb’’. So I replaced that resistor with a
tiny bulb (a much smaller, kind of those used in the
dashboards), also in parallel with the LED and IT DID fool
the OBC. It’s just a guess, but I believe the much modern
BMW system checks the bulb resistance when it is NOT lit,
which is a much lower value. As said, just my guess.–
The original message included these comments:

That whole idea is just laughable. You can buy resistors made just
for this, but when you see how much they want for them you’ll gag.
So, the most plausible thing to use for a resistor is – a light
bulb. Just take the light bulb you removed from the socket and wire


Luis Gasperini / '91 V12 XJ-S conv. 5sp
Montevideo, Uruguay
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Luis Gasperini wrote:

Don’t know exactly which expensive ‘‘made for this’’ resistors
you mean Kirby, and would like to know.

Heck, I dunno any more. Looked 'em up online about 5 years ago when
I was considering some LED turn signal bulbs for my Mazda. Quickly
ditched that idea when I found the things were so expensive. The
LED’s resulted in the blinkers blinking double-speed, which is the
bulb failure indication in this car. And it turned out to be built
into the flasher unit itself, which also contained the hazard warning
flasher scheme. I was able to do some tricky rewiring to install a
generic “heavy duty” flasher with no bulb failure warning feature to
get my turn signals back to a reasonable flash rate. It still uses
the OEM flasher for hazard warnings.

I put LEDs in a BMW and installed in parallel common cheap
resistors. Don’t remember exactly, but something around 35
Ohm, which was what gave the same current as the removed
bulb.

35 ohms sounds about right for a running light bulb – but of course
you’d need two, or however many bulbs are in the taillights. For my
turn signal bulb, the wattage is higher so the ohmage is lower.
Either way, though, the resistor must be able to handle the wattage,
which means a little 1/2 watt resistor won’t do.

Yet it didn’t fool the on-board computer which kept on
displaying ‘‘burnt bulb’’. So I replaced that resistor with a
tiny bulb (a much smaller, kind of those used in the
dashboards), also in parallel with the LED and IT DID fool
the OBC. It’s just a guess, but I believe the much modern
BMW system checks the bulb resistance when it is NOT lit,
which is a much lower value. As said, just my guess.

That’s pretty tricky! D’ya suppose they came up with that scheme
just to prevent the installation of LED’s?

– Kirbert

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In reply to a message from Kirbert sent Tue 1 Dec 2009:

i fitted led bulbs and the bulb warning light came on. so I
by-passed the offending relay. who needs it anyway?–
rex
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In reply to a message from Kirbert sent Tue 1 Dec 2009:

Of course I used one such resistor per LED, and they were
similar to this one:

therefore capable of handling the power at 12V. But it did
not fool the computer, though it drew about the same amps
than the original bulb. But, (as already said), a smaller
bulb in parallel with the LED DID FOOL the computer, though
it drew less amps than the original bulb.

What I’m GUESSING is that the OBC does not check the drawn
current, but maybe the resistance of the circuit with the
lights off, which is by FAR a lower value than those 35
Ohms. You can check that, by measuring the bulb resistance
with a digital multimeter.–
The original message included these comments:

35 ohms sounds about right for a running light bulb – but of course
you’d need two, or however many bulbs are in the taillights. For my
turn signal bulb, the wattage is higher so the ohmage is lower.
Either way, though, the resistor must be able to handle the wattage,
which means a little 1/2 watt resistor won’t do.
That’s pretty tricky! D’ya suppose they came up with that scheme
just to prevent the installation of LED’s?


Luis Gasperini / '91 V12 XJ-S conv. 5sp
Montevideo, Uruguay
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Just a thought, maybe it senses the surge current that occurs prior to the
fillament heating and the resistance increaseing… That being the case
perhaps the ideal may be to wire a large capacitor across the light power
feed and ground to simulate the initial current surge as it charges…
Just my two cents worth

Duncan

82 XJS-----Original Message-----
From: owner-xj-s@jag-lovers.org [mailto:owner-xj-s@jag-lovers.org]On
Behalf Of Luis Gasperini
Sent: Thursday, 3 December 2009 11:49 a.m.
To: xj-s@jag-lovers.org
Subject: Re: [xj-s] change running lights to LED’s

In reply to a message from Kirbert sent Tue 1 Dec 2009:

Of course I used one such resistor per LED, and they were
similar to this one:

therefore capable of handling the power at 12V. But it did
not fool the computer, though it drew about the same amps
than the original bulb. But, (as already said), a smaller
bulb in parallel with the LED DID FOOL the computer, though
it drew less amps than the original bulb.

What I’m GUESSING is that the OBC does not check the drawn
current, but maybe the resistance of the circuit with the
lights off, which is by FAR a lower value than those 35
Ohms. You can check that, by measuring the bulb resistance
with a digital multimeter.

The original message included these comments:

35 ohms sounds about right for a running light bulb – but of course
you’d need two, or however many bulbs are in the taillights. For my
turn signal bulb, the wattage is higher so the ohmage is lower.
Either way, though, the resistor must be able to handle the wattage,
which means a little 1/2 watt resistor won’t do.
That’s pretty tricky! D’ya suppose they came up with that scheme
just to prevent the installation of LED’s?


Luis Gasperini / '91 V12 XJ-S conv. 5sp
Montevideo, Uruguay
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–
–Support Jag-lovers - Donate at http://www.jag-lovers.org/donate04.php

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Luis Gasperini wrote:

What I’m GUESSING is that the OBC does not check the drawn
current, but maybe the resistance of the circuit with the
lights off, which is by FAR a lower value than those 35
Ohms.

Hey, that makes sense. Yes, resistance rises with temperature and
that filament runs really hot, so the resistance of a light bulb when
off is very low indeed. If the 'puter just sends some tiny current
to the bulb when off to check for “continuity”, having a 35 ohm
resistor in there could make it decide the bulb is burnt out.

– Kirbert

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