Resisters for 1W led in Fogs

phatchink · 10-09-2007

So I'm trying to replace my Fog lamps to a 1W LED bulb, but I'm unsure of what resister to use. I've red noregret4life's pdf but there's no real formula to calculate what resister I would need. Can anyone shed some light on this? Possibily noregret4life.

The reason why i'm doing this is because I live in the city and there's no real need for the fogs, so instead of spending $ on hids (and more $ to disable the directional lamps) I would like to just replace it will good looking LED bulbs.

http://www.slkworld.com/general-modi...-tutorial.html

**etyu** · 10-09-2007

How about using Sylvannia Silverstar aftermarket H7 halogen lamps with a color temp of 4100 K? You won't need resistors.

cyberdrakon · 10-09-2007

I would suggest wiring seperate LEDS (drill small hole, glue in) and wire it with the side indicator lights, this way you won't loose the foglight functionaliy...and you can leave the light switch on automatic.

phatchink · 10-10-2007

Here are the LEDs i'm referring to, I dont know about drilling holes, i doubt i can ever get them to align properly, plus I've tried the 4100ks and they still look very yellowish after I've turned my headlights on.
http://cgi.ebay.com/ebaymotors/V-LED...8722QQtcZphoto

**etyu** · 10-10-2007

The LED's on the ebay link are Daylight Running Lamp at 1W. This would be okay if it is only for looks but not for function (i.e., they won't function to shed light on the road ahead in a fog).

noregret4life · 10-11-2007

phatchink, you have a few choices here...

To achive 100% best results, you should install an HID kit into your fog lights like i did. you get 100% color and 1000% more usability than the LED option. I can not begin to explain the difference in light output when you have Stock HIDs for low beams and HID kit for fog lights.

Obviously 2 things come into play here... #1 do you have cornering foglights? #2 are you willing to spend around $150-170 for an HID kit?
My tutorial explains the cornering fog lights bit and the adapters needed. If you don't have cornering fog lights, then it's even easier to install.

Next... if you do not want to spend the money on an HID upgrade, you can use these LED 1W bulbs, but i do not see this as a long term solution. 1W LEDs pop like microwave popcorn

So you will be changing them out if you get unlucky within 4 months. Sometimes this is not the case and they do run fine for a very long time. Regardless think Wattage output... Stock fog lights are 55w vs 1w LED... Next the LEDs are forward firing... which means that your foglight will only partially be lit up. The led faces forward and will only bounce light back to the reflector off the front glass. What this means is that you will have just a single bright dot with some ambient light glowing around it...

Another thing you should know about LEDs is that they are not all the same color Temp. So what this means is that if you buy 5x1W leds from different suppliers or even the same supplier, you may get slight differences in color output. AND NOT MATCH THE HID LOW BEAMS exactly. Sure they will look white, Much whiter that stock, but may not be exact HID 4300K color temp.

On the subject of resistors, if you choose to use these LED bulbs. Your current stock fog lights are 55w and 12v.

Now a little bit of math and Ohm's Law...

P = Power in Watts
E = Volts
I = Electrical Current in Amps
R = Electrical Resistance in Ohms

Ohm's Law Base Formula: P=I*E or E=I*R

To find RESISTANCE: R=(E^2)/P

We know the P (55watts stock bulbs) and we know the E (12volts)

so... R=144/55, Resistance=2.618 Ohm

Now, here is what you must consider...
#1 you may not find exactly 2.618Ohm & 55W resistors on the market
#2 you do NOT need to be exact in this case
#3 the Mercedes lighting computer seeks resistance at a much lower value, so what this means is that you can get away with using a lower Watt resistor (5w/27ohm) may be enough to trick the lighting computer into thinking that a bulb is in there.

Next, selecting the resistor type. YOU WILL NEED TO USE ALUMINUM cased resistors. for such high wattage, this is a MUST! They will get very hot (think of toaster ovens..they use resistance wires to heat your food!!!) and they MUST be away from all plastic and wiring.

Hope this helps... any questions message me or email

msfamilia · 10-12-2007

I am so interested in this mod!!!!!

Honestly at where I live, I cannot care less about the lighting output of my foglight. The HID low beam is already bright enough for anytime I need to see. So having a white dot in my fog housing would be a very neat idea.

Lenny, I do not understand about the lower watt resistor part. So a 5w/27 ohm resistor is already enough to shut up the warning light on the cluster? as opposite to 2.61~ Ohm & 55W resistor (that maybe impossible to find) ?

where do you think I can find a 5w/27ohm resistor? or is that any other resistors(the w/ohm reading) that will be a safer bet for the warning not to show?

noregret4life · 10-12-2007

V-LED sells load resistors. However i am a little confused as to how they are doing their calculations for the Watts/Ohms/Ambs.

http://cgi.ebay.com/ebaymotors/LED-T...8884QQtcZphoto

Either way. I suggest being as close as possible to a real life bulb when getting a resistor installed on the line. Which means go for a 50-55watt resistor with 2.6 ohms as i described above. I have used my above calculation to install resistors all over my car for the 5w bulbs, and no issues thus far. Even the MB tech at my dealership said that i have no errors on the computer (even though i completely removed a few bulbs and left just resistors)

phatchink · 10-13-2007

hi noregret4life, thank you very much for the wonderful tutorial, I know what Imust do now. Yes I do have the corning lights so tahts why i opted to go with the 1W LED method. I was originally gogin to get HIDs, but to get my car to the dealer and paying them to disable that option is too much a waste of my time and money imo so thats why i'm going to do this instead.

thank you again.!

**etyu** · 10-13-2007

Quote:

Originally Posted by phatchink

hi noregret4life, thank you very much for the wonderful tutorial, I know what Imust do now. Yes I do have the corning lights so tahts why i opted to go with the 1W LED method. I was originally gogin to get HIDs, but to get my car to the dealer and paying them to disable that option is too much a waste of my time and money imo so thats why i'm going to do this instead.

thank you again.!

Please post detailed pictures if possible when you do your modification.

Have fun doing the mod.

msfamilia · 10-17-2007

thanks Lenny
and phatchink, I found this site selling LED bulbs in H7 size which should be the correct size for our car.

http://www.superbrightleds.com/cgi-b...gi?product=CAR

Have you decided where do you get your resistor yet?

noregret4life · 10-21-2007

Quote:

Originally Posted by msfamilia

thanks Lenny
and phatchink, I found this site selling LED bulbs in H7 size which should be the correct size for our car.

http://www.superbrightleds.com/cgi-b...gi?product=CAR

Have you decided where do you get your resistor yet?

For the resistors i would check out one of the large online retailers like http://www.mouser.com/ Check out the ones made by Vishay/Dale. I think you will find what you need there.

msfamilia · 10-23-2007

Quote:

Originally Posted by noregret4life

For the resistors i would check out one of the large online retailers like http://www.mouser.com/ Check out the ones made by Vishay/Dale. I think you will find what you need there.

So just to confirm, I need something that is 50-55watt resistor with 2.6 ohms, am I correct?

noregret4life · 10-23-2007

Yes, you are correct. However you also should make sure they are aluminum housed.

10-09-2007	#1 (permalink)
phatchink Senior SLK World Member Join Date: Dec 2006 Posts: 123 Country: Thanks: 0 Thanked 0 Times in 0 Posts	Resisters for 1W led in Fogs So I'm trying to replace my Fog lamps to a 1W LED bulb, but I'm unsure of what resister to use. I've red noregret4life's pdf but there's no real formula to calculate what resister I would need. Can anyone shed some light on this? Possibily noregret4life. The reason why i'm doing this is because I live in the city and there's no real need for the fogs, so instead of spending $ on hids (and more $ to disable the directional lamps) I would like to just replace it will good looking LED bulbs. http://www.slkworld.com/general-modi...-tutorial.html

10-09-2007	#2 (permalink)
etyu Founding Member #2 / Ambassador Of Good Will Join Date: Jun 2006 Location: Orange County, CA Vehicle: 2008 SLK 55 Posts: 5,281 Country: Thanks: 377 Thanked 277 Times in 168 Posts	How about using Sylvannia Silverstar aftermarket H7 halogen lamps with a color temp of 4100 K? You won't need resistors. __________________ *Eddy* To view links or images in signatures your post count must be 5 or greater. You currently have 0 posts. Pewter/Beige, PIII package, Airscarf, Hands-Free Communication System, Lighting package Designo Black Leather Cover on e-brake handle, ( To view links or images in signatures your post count must be 5 or greater. You currently have 0 posts. Bill T), SmartTop v1.0, Kleyman 3BFM (NoRegret Custom), Green Air Filters, *Mod. R170 ant.*, EuroClear sidemarkers w/PIAA PlasmaIon lamps, chromed front & rear turn indicator lamps, PIAA SuperPlasmaGTX front parking lamps, bilateral rear fog lamps enabled.

10-10-2007	#5 (permalink)
etyu Founding Member #2 / Ambassador Of Good Will Join Date: Jun 2006 Location: Orange County, CA Vehicle: 2008 SLK 55 Posts: 5,281 Country: Thanks: 377 Thanked 277 Times in 168 Posts	The LED's on the ebay link are Daylight Running Lamp at 1W. This would be okay if it is only for looks but not for function (i.e., they won't function to shed light on the road ahead in a fog). __________________ *Eddy* To view links or images in signatures your post count must be 5 or greater. You currently have 0 posts. Pewter/Beige, PIII package, Airscarf, Hands-Free Communication System, Lighting package Designo Black Leather Cover on e-brake handle, ( To view links or images in signatures your post count must be 5 or greater. You currently have 0 posts. Bill T), SmartTop v1.0, Kleyman 3BFM (NoRegret Custom), Green Air Filters, *Mod. R170 ant.*, EuroClear sidemarkers w/PIAA PlasmaIon lamps, chromed front & rear turn indicator lamps, PIAA SuperPlasmaGTX front parking lamps, bilateral rear fog lamps enabled.

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10-09-2007	#3 (permalink)
cyberdrakon Elite SLK World Member Join Date: Jun 2006 Location: SoCal, USA Vehicle: SLK55 2006 Other Toys: 560SEC 1990, CLK500 2005 Posts: 1,400 Country: Thanks: 24 Thanked 63 Times in 42 Posts	I would suggest wiring seperate LEDS (drill small hole, glue in) and wire it with the side indicator lights, this way you won't loose the foglight functionaliy...and you can leave the light switch on automatic.

10-10-2007	#4 (permalink)
phatchink Senior SLK World Member Join Date: Dec 2006 Posts: 123 Country: Thanks: 0 Thanked 0 Times in 0 Posts	Here are the LEDs i'm referring to, I dont know about drilling holes, i doubt i can ever get them to align properly, plus I've tried the 4100ks and they still look very yellowish after I've turned my headlights on. http://cgi.ebay.com/ebaymotors/V-LED...8722QQtcZphoto

10-11-2007	#6 (permalink)
noregret4life Elite SLK World Member Join Date: Jun 2006 Location: NJ Vehicle: '05 SLK350 Posts: 1,092 Country: Thanks: 1 Thanked 17 Times in 11 Posts	phatchink, you have a few choices here... To achive 100% best results, you should install an HID kit into your fog lights like i did. you get 100% color and 1000% more usability than the LED option. I can not begin to explain the difference in light output when you have Stock HIDs for low beams and HID kit for fog lights. Obviously 2 things come into play here... #1 do you have cornering foglights? #2 are you willing to spend around $150-170 for an HID kit? My tutorial explains the cornering fog lights bit and the adapters needed. If you don't have cornering fog lights, then it's even easier to install. Next... if you do not want to spend the money on an HID upgrade, you can use these LED 1W bulbs, but i do not see this as a long term solution. 1W LEDs pop like microwave popcorn So you will be changing them out if you get unlucky within 4 months. Sometimes this is not the case and they do run fine for a very long time. Regardless think Wattage output... Stock fog lights are 55w vs 1w LED... Next the LEDs are forward firing... which means that your foglight will only partially be lit up. The led faces forward and will only bounce light back to the reflector off the front glass. What this means is that you will have just a single bright dot with some ambient light glowing around it... Another thing you should know about LEDs is that they are not all the same color Temp. So what this means is that if you buy 5x1W leds from different suppliers or even the same supplier, you may get slight differences in color output. AND NOT MATCH THE HID LOW BEAMS exactly. Sure they will look white, Much whiter that stock, but may not be exact HID 4300K color temp. On the subject of resistors, if you choose to use these LED bulbs. Your current stock fog lights are 55w and 12v. Now a little bit of math and Ohm's Law... P = Power in Watts E = Volts I = Electrical Current in Amps R = Electrical Resistance in Ohms Ohm's Law Base Formula: P=IE or E=IR To find RESISTANCE: R=(E^2)/P We know the P (55watts stock bulbs) and we know the E (12volts) so... R=144/55, Resistance=2.618 Ohm Now, here is what you must consider... #1 you may not find exactly 2.618Ohm & 55W resistors on the market #2 you do NOT need to be exact in this case #3 the Mercedes lighting computer seeks resistance at a much lower value, so what this means is that you can get away with using a lower Watt resistor (5w/27ohm) may be enough to trick the lighting computer into thinking that a bulb is in there. Next, selecting the resistor type. YOU WILL NEED TO USE ALUMINUM cased resistors. for such high wattage, this is a MUST! They will get very hot (think of toaster ovens..they use resistance wires to heat your food!!!) and they MUST be away from all plastic and wiring. Hope this helps... any questions message me or email

10-12-2007	#7 (permalink)
msfamilia Senior SLK World Member Join Date: Mar 2007 Location: SF Bay Area Vehicle: 2005 SLK 350 Posts: 119 Country: Thanks: 0 Thanked 0 Times in 0 Posts	I am so interested in this mod!!!!! Honestly at where I live, I cannot care less about the lighting output of my foglight. The HID low beam is already bright enough for anytime I need to see. So having a white dot in my fog housing would be a very neat idea. Lenny, I do not understand about the lower watt resistor part. So a 5w/27 ohm resistor is already enough to shut up the warning light on the cluster? as opposite to 2.61~ Ohm & 55W resistor (that maybe impossible to find) ? where do you think I can find a 5w/27ohm resistor? or is that any other resistors(the w/ohm reading) that will be a safer bet for the warning not to show?

10-12-2007	#8 (permalink)
noregret4life Elite SLK World Member Join Date: Jun 2006 Location: NJ Vehicle: '05 SLK350 Posts: 1,092 Country: Thanks: 1 Thanked 17 Times in 11 Posts	V-LED sells load resistors. However i am a little confused as to how they are doing their calculations for the Watts/Ohms/Ambs. http://cgi.ebay.com/ebaymotors/LED-T...8884QQtcZphoto Either way. I suggest being as close as possible to a real life bulb when getting a resistor installed on the line. Which means go for a 50-55watt resistor with 2.6 ohms as i described above. I have used my above calculation to install resistors all over my car for the 5w bulbs, and no issues thus far. Even the MB tech at my dealership said that i have no errors on the computer (even though i completely removed a few bulbs and left just resistors)

10-13-2007	#9 (permalink)
phatchink Senior SLK World Member Join Date: Dec 2006 Posts: 123 Country: Thanks: 0 Thanked 0 Times in 0 Posts	hi noregret4life, thank you very much for the wonderful tutorial, I know what Imust do now. Yes I do have the corning lights so tahts why i opted to go with the 1W LED method. I was originally gogin to get HIDs, but to get my car to the dealer and paying them to disable that option is too much a waste of my time and money imo so thats why i'm going to do this instead. thank you again.!

10-17-2007	#11 (permalink)
msfamilia Senior SLK World Member Join Date: Mar 2007 Location: SF Bay Area Vehicle: 2005 SLK 350 Posts: 119 Country: Thanks: 0 Thanked 0 Times in 0 Posts	thanks Lenny and phatchink, I found this site selling LED bulbs in H7 size which should be the correct size for our car. http://www.superbrightleds.com/cgi-b...gi?product=CAR Have you decided where do you get your resistor yet?

10-23-2007	#14 (permalink)
noregret4life Elite SLK World Member Join Date: Jun 2006 Location: NJ Vehicle: '05 SLK350 Posts: 1,092 Country: Thanks: 1 Thanked 17 Times in 11 Posts	Yes, you are correct. However you also should make sure they are aluminum housed.

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