Need specs for resustors
Thread Starter
Junior Member
Joined: Jul 2025
Posts: 16
Likes: 1
2005 C240 w203
Need specs for resustors
Hey all,
Need specs to get resistors for OEM HID headlamps.
2005 C240 with halogen headlamps, installed OEM HID headlamps. Don't have the funds to purcha xentry or STAR, so I'm going to install resistors.
Poured over the massive number of posts regarding this, and could bot dind a definitive answer.
TIA!!
Need specs to get resistors for OEM HID headlamps.
2005 C240 with halogen headlamps, installed OEM HID headlamps. Don't have the funds to purcha xentry or STAR, so I'm going to install resistors.
Poured over the massive number of posts regarding this, and could bot dind a definitive answer.
TIA!!
Last edited by SCFNH; Oct 2, 2025 at 11:52 AM.
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Joined: Dec 2003
Posts: 3,275
Likes: 236
From: BC, Canada
2003 C230K Coupe Orion Blue
Have you tried going to an indie? They can change the required settings for a nominal fee, and are usually way cheaper than the dealership.
If you still want to go the resistor route, it can be done with a little bit of electrical knowledge.
The stock halogens draw 55W. There's a certain amount of wattage (or amperage) the lights needs to draw or it'll throw an error. Unfortunately nobody knows what the exact number is (and it may vary between individual cars) so you'll have to do a bit of experimentation. The OEM HIDs draw 35W, so you'll have to make up some kind of shortfall. The car doesn't require the full 55W. Personally I'd start with the assumption of 0.5 x (55 - 35) = 10W, then go from there.
For my calculations I use 12.0V and 14.0V which is often what the car sees while parked and during normal operation respectively. Using Ohm's law, (14^2) / 10 = 19.6 ohms. Knowing this, start with something around 20-30 ohms, and use 20W resistors (best to use 2x expected power draw for sizing resistors). Personally I'd start fiddling with the various resistor values and slowly increase until the car throws an error, then back off a bit for the final resistor value selection. Draw too little juice and the car throws an error. Draw too much juice and the resistors run hotter than necessary.
If you still want to go the resistor route, it can be done with a little bit of electrical knowledge.
The stock halogens draw 55W. There's a certain amount of wattage (or amperage) the lights needs to draw or it'll throw an error. Unfortunately nobody knows what the exact number is (and it may vary between individual cars) so you'll have to do a bit of experimentation. The OEM HIDs draw 35W, so you'll have to make up some kind of shortfall. The car doesn't require the full 55W. Personally I'd start with the assumption of 0.5 x (55 - 35) = 10W, then go from there.
For my calculations I use 12.0V and 14.0V which is often what the car sees while parked and during normal operation respectively. Using Ohm's law, (14^2) / 10 = 19.6 ohms. Knowing this, start with something around 20-30 ohms, and use 20W resistors (best to use 2x expected power draw for sizing resistors). Personally I'd start fiddling with the various resistor values and slowly increase until the car throws an error, then back off a bit for the final resistor value selection. Draw too little juice and the car throws an error. Draw too much juice and the resistors run hotter than necessary.
Last edited by slammer111; Oct 2, 2025 at 06:48 PM.
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Joined: Jun 2002
Posts: 7,266
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From: So. Oregon Coast
C230 Sport Coup + 2006 W164 ML350 + 99 Ford Escort RIP
You'lll need monster resistors capable of 20 watts or more.
More is better. These puppies are likely to be red hot so they need to be mounted accordingly.
Isnt there cables sold dedicated to this purpose that fool the ECU in the same way the newer
CANBUS compatible LED's do?
I know how hard it can be to a.) find a tech with SDS and then
b.) get them to do any modifications to the ECU. Mine
would not believe it was ok to do the change while still having Halogens.
But eventually I conovinced him. Plus I fixed one of his anciennt Dell PC's used for
SDS replaced the BIOS battery which cost $20 for the stinking battery!
More is better. These puppies are likely to be red hot so they need to be mounted accordingly.
Isnt there cables sold dedicated to this purpose that fool the ECU in the same way the newer
CANBUS compatible LED's do?
I know how hard it can be to a.) find a tech with SDS and then
b.) get them to do any modifications to the ECU. Mine
would not believe it was ok to do the change while still having Halogens.
But eventually I conovinced him. Plus I fixed one of his anciennt Dell PC's used for
SDS replaced the BIOS battery which cost $20 for the stinking battery!
Thread Starter
Junior Member
Joined: Jul 2025
Posts: 16
Likes: 1
2005 C240 w203
Well, despite my atrocious spelling, I did get this sorted out.
Finally found a garage that was willing to go out on a limb and just jump in with both feet!!!
If you're in the New England area, please patronize https://www.603mtech.com/
They are in Hooksett, NH and are top notch customer service oriented!!! Can't speak highly enough for Mike and his crew!! Be sure to bring dog biscuits tho!!
Finally found a garage that was willing to go out on a limb and just jump in with both feet!!!
If you're in the New England area, please patronize https://www.603mtech.com/
They are in Hooksett, NH and are top notch customer service oriented!!! Can't speak highly enough for Mike and his crew!! Be sure to bring dog biscuits tho!!
MBWorld Fanatic!
Joined: Jun 2002
Posts: 7,266
Likes: 170
From: So. Oregon Coast
C230 Sport Coup + 2006 W164 ML350 + 99 Ford Escort RIP
So you found a shop who could do the coding??
FYI- Here's the sequence in SDS
1. EIS- Electronic Ignition Switch
2. Control Unit Adapations
3. Read Coding and change if necessary
4. All Codes
5. Xenon Headlamp- (Change to "present")
FYI- Here's the sequence in SDS
1. EIS- Electronic Ignition Switch
2. Control Unit Adapations
3. Read Coding and change if necessary
4. All Codes
5. Xenon Headlamp- (Change to "present")
