TheRulesLawyer

W204 2012 2013 2014 facelift rear brake reverse tail lights led wiring pin (So future searches will find this)

When changing out the incandescent bulbs for LED 99% of them will likely cause a canbus fault with your lights. They'll work, but you'll have to cancel it every start. You can add load resistors to fix this.

I mapped the pins for LED load resistors on my 2012 c350.
https://i.imgur.com/mEcI7wX.jpg

Brown is G- ground
2-4 are the other existing LED tail lights. If you have a pre face lift you may use them, but I can't test.
5, 6 are lower brake lights
7 is the reverse light

You need 6x . 1 per light.
I used and

• I wired all ends to one wire and soldered then attached to the negative wire with T taps I didn't want to try and tap the ground more than needed.
• The Wires you need are the furthest from the ground.
• Doesn't really matter the order you tap them.
• Order is mirrored left to right on other side. Just pick the furthest from brown.
• I mounted the resistors to metal with 3m VHB tape. you'll need 1/2" for the common resistors for this.

Not super hard, but I couldn't find the pinout anywhere for this.

C300CA

Mine is 2011 C300, all the rear lights are converted to LEDs and only backup lights need resistors to avoid error messages. Front lights except low beam headlights are all LEDs too, no load resistors no error messages. Low beam headlight don't need load resistors with LEDs. I haven't found or decided to use LED or HID that's why I leave it stock now. Looks like before and after facelift is different.