chuckpaertz

What is the wiring sequence for 2012 GLK tail light module? I need to a load resistor to remove the dash bulb out warning. Picture is of Right assembly.

tonytag25

did you ever figure this out?

John CC

You need a resistor that will draw about the same current as the original bulb and has the wattage rating at least as high as the original bulb.

Divide the wattage of the original bulb by 14 to get the current, so, if the bulb was a 25 watt bulb, 25 divided by 14 (the system voltage) is about 2. You need 2 amps of current through the resistor to trick the bulb minder circuit. Divide 14 by 2 (the current) to get the resistance, 7 ohms (6 is close enough). So, you need a resistor with about 6 ohms and at least a 25 watt rating. A better way to calculate the wattage is 14*14 divided by the resistance, or 196/6 = 33. (This is a clue that we really could get away with a higher resistance).

If you're like me, you'll consider that the LED bulb is drawing some current, probably about 1/4 to 1/3 of the current the old bulb draws, so you round the resistance up, say to 8, which gets your wattage below 25. You can also adjust your initial current calculation to consider the current of the LED bulb, so, e.g. take 3/4 of the 2 amps, and get 1-1/2 amps. Divide 14 by 1.50 and get 9.3 Ohms, which you could probably round up to 10. Now your wattage calculation, 196/10, gets you 19.6, safely within the capacity of a 25 watt resistor.

If you can mount the resistors on a metal panel, the wattage is less critical. If not, I'd use 50 watt resistors for the above example. The wattage is converted to heat by the resistor.

Now, the easy part: connect one end of the resistor to the hot wire for the lamp in question, and the other end to the ground for the light assembly. (Any ground will probably work, but these circuits are sensitive, so, better safe than sorry.)

tonytag25

@John CC
I followed this forum below:
https://mbworld.org/forums/glk-class...S6wwCZ4w7-iyoA

I put 6 ohm 50 Watt resistors on the 3 wires which get "swapped" in the harness but I suppose this is wrong?

tonytag25

John CC

I don't know what those wires do, so I can't say. When you say "I put 6 ohm 50 Watt resistors on the 3 wires" I'm not sure what that means, either. Did you use two resistors or three? Where did you put the other end of the resistor?

The brown wire is the ground in the harness above. One end of each resistor should connect there.

tonytag25

@John CC

I added the resistor to the lines that were swapped so I spliced the lines after re-pinning them and add the resistor in those lines mentioned in the other thread. To my understanding, the brown line is the hotline, so that’s what supplies power to the entire assembly, my tail lights work and function as intended. The only issue is the error messages that I have on my dashboard and that I have the fog light warning for the rear tail light and my understanding there’s only one side that illuminates for the rear tail light fog light, which is the driver side so, when my car turns on the headlights in automatic mode, my tail lights will turn on, and that fog light stays illuminated on the driver side in the rear

John CC

Do you mean you cut the wire then attached one cut end to each end of the resistor? That is wrong. You have reduced the current rather than increasing it, to the point where the LEDs won't light, I'm guessing.

Brown is always ground in Mercedes. You need to identify the various hot leads for the lights that are giving the errors (I may have some notes somewhere) then tap one end of a resistor onto each one and tap the other end on to the brown wire. 3 way taps are often used, and often provided with the resistors.

John CC

Here's a picture:

tonytag25

Yes, that’s correct. I got the wires and added the resistor between the supply and the light itself. I do still work, but I added a load which reduces the current.

OK, I think I’m understanding it now. But in this fashion, you would ground only be the three lines that are on the LED lines and split 3 way. According to that forum I’m assuming.

John CC

Here's a post on the factory wiring: (Link doesn't work...)

Here's my notes:
Brown: Ground
Blue/Grey: Reverse
Black/Red: tail light only bulb
Green: ??
Black/White: Left Turn
Pink: PWM tail and brake bulb
On the passenger side the turn signal is Black/Green.

tonytag25

this is for the headlight though right?

but I think I see the idea here if you jump the wires and I'm assuming the black wire is your ground. I used these exact same resistors

John CC

What lights are you working with?

John CC

Assuming the three wires you cut are the hots for the three lamps that need resistors, reconnect the cut ends and add one end of a resistor to each of the three. Then, without cutting the brown wire, connect the other end of each of the three resistors to the brown wire.

John CC

In the photo the black wire is probably ground and the green one is hot. I think it's a turn signal bulb. It's just a picture I grabbed off the internet to show how the wiring is done relative to the factory leads.

John CC

Assuming the three wires you cut are the hots for the three lamps that need resistors, this is how you'd want to do it:

trigital

Resistors consume the difference of energy needed for not triggering the Cluster Fault Code, generating Heat. Why anyone will want excessive heat only for a fault code.

Usually, this job only need a very cheep coding for Rear SAM.

tonytag25

Yes this is exactly what I'm going to do tomorrow. I will post the pictures and results