I did this mod 2 months ago and it has been working great so far. I got 2 festoons from ebay and I used 2 10ohm resistors for each bulb.

Great post and 100% correct.
One detail here is that you do not need to match the resistance of the OEM bulb, you only need enough resistance to fool the cars computer. The ideal situation is to use the largest value resistor that prevents bulb out warning.
What you are trying to avoid is having a red hot resistor anywhere in your car.

For example,
A 100 Ohm 10 amp ceramic resistor used in the License plate circuit will only get warm to the touch.

A 10 Ohm 10 amp ceramic resistor used in the license plate circuit will burn your hand in less than 30 seconds, bad bad bad. If you want a fire hazard this is it.

So in your test phase, make sure to check how hot your resistors get after 10, 20, 30 minutes if you can not touch them, Do not use them.

BTW my leds have lasted 20 months. (non china at the time) spectrumled . com

so im installing this mod right now, and both lights were working at first, but after i plugged in the resistor, both lights went out, and after i unplugged the resistors, they still wont turn back on

i wasnt really sure how to hook up the resistors, so do u guys think i might have blown out the LEDs some how buy not hooking up the resistor right??

Check your fuses. You may have blown one since its not working at all.

ya so i was working on these lights in the morning, and tonight when i was driving home, i noticed that the climate control, the radio, and the instrument cluster lights all didnt work when i turned the lights on, so im guessing a fuse blew, but i cant figure out which one it is, i saw two fuses on the fuse box cover that said instrument cluster, radio, and climate control, and i took one out and it made it so the needles didnt move on the cluster, then i took the other one out and it turned off all of the lights in the cluster...so do u guys know which fuse is the one which is for the instrument cluster, the radio, and the climate control?? so im guessing that the license plate lights are connected to the same fuse as the instrument cluster lights??

I dont know where the fuse is but it wont hurt to check all the fuses in the car. There is a fuse box under the rear seat near the battery, on the drivers side dash, and there is one under the hood on the drivers side.

check fuse #11 on the drivers side dash. That is the one for the licence plate/instrument cluster bulbs

hey thanks a lot...i figured it out, it was the #11 fuse and i replaced it, now all the lights work

BRINGING IT BACK FROM THE DEAD

guys I need for someone to explain, much better a picture, on how to install a resistor..

I keep hearing just twist the resistor cables around the bulb socket but I dont understand it...

that picture says its showing me how to do it but my car is not like that

In mine I only take off the plastic cover and the bulb is attached to it... do I have to take out the whole fixture to expose the "bulb socket" ?

yes

so that picture right there is not ONLY the plastic cover, its the WHOLE fixture

Yes, one does not typically attach wires to a plastic cover, right?

but I dont think my fixture looks anything like that once off. On mine when u take off the plastic lid on u expose these two metals what look like "claws" that hold the bulb.. is that where I must attach the resistor?

I'm not sure which part of this you are not understanding. The part pictured is from an older W210. You have a newer W203. They may be slightly different parts, but they work the same way.

If you take off the plastic cover and see the bulb, you have not removed the entire fixture. The Resistor goes on the connection from the wires to the fixture. Not between the bulb and the fixture.

yup, after a hour its all good, had to remove the whole trunk insert. Didnt have to split or strip wires, working perfect thanks MG!

Superbrightleds.com has everything! love that place