# using bulbs with different current

• posted on November 27, 2006, 12:42 pm
If I replace my 6w sidelights with longer life LED bulbs taking a few milliamps, presumably the ship-board computer will think the bulbs have blown and will continue to annoy me by saying so every time I turn them on.
Is there a way to tell the computer to expect low current drain from the sidelights and not flag an error?
year 2000 E320 cdi
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• posted on November 27, 2006, 1:19 pm
Nihil wrote:

Yes, put an inline resistor of the difference and that will make the Headlight relay believe the normal bulb is in there. If the LED's fail it will still show a drop and the light will come on.
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• posted on November 27, 2006, 2:31 pm
The normal bulb takes about 0.5 Amp And the LED probably 0.05 Amp So the resistor in parallel with the led must take about 0.45 Amp to appear normal, say 27ohm, and dissipate about 6 Watts.it may get as hot as a bulb.
If the LED fails, assuming it goes open circuit, the current will change by 0.05Amp and I doubt the computer will detect this.
I also doubt that Mercedes have the possible use of LED's programmed into the current range of cars yet.
But it will come soon, probably with a model change and possibly with the change to 42Volts which has often been suggested.
Alec

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• posted on November 28, 2006, 4:51 am

You meant to say in Series right?
gamini
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• posted on November 28, 2006, 4:39 pm
No
There will be a resistor in series with the LED but if it is a 12V LED it will be inside the LED. If it is not a 12V LED the you will have to add a resistor to limit the LED current.
I was referring to a resistor in parallel with the LED (or LED with series resistor) which is added to deceive the car computer into thinking that a normal bulb is fitted.
Alec

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• posted on November 28, 2006, 6:21 pm
Alec wrote:

Thanks to all from the originator of this post. I understand that a resistor in parallel to shunt 0.5 amp would fool the computer into thinking there would be a normal bulb there. And, yes, there will be another resistor insider the LED, but this is not my concern.
The trouble with this is that
1 an external parallel resistor would be difficult to install on the wiring loom, 2 there would be no warning of a bulb failure, though LEDs last a long time.
I had thought that I read in a thread on Xenon headlight bulbs that it was possible to tell the computer to use different limits of acceptable current. Is this really not possible?
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• posted on November 29, 2006, 9:42 am
Sorry I do not have any info on the capabilities or reprogramability of the in car computer.
Alec