Brown is ground. Must have ground for any lights to work.

The extra wire is probably for a running light bulb in the main headlight area. US market has running lights on the front side markers.

 

So I have to relocate the brown wire? Which wire do I not need ? Like I know I don’t need the city light . Idk which one is which. Chat gpt is fkn retarded

 

Yeah it's not about # of wires, it about what wire does what.

Your 4 pin connector looks like it has 3 wires. You know brown = grnd. run a wire from other wires to headlight and see which one lights things up.

AI sez: (I only post so that you can learn from it - may) not be 100%)


US headlights use separate bulbs and sockets; Euro headlights combine low and high beams in an H4 or H5 bulb.


Euro headlight pinout (typical 6-pin):

1. Low beam (+)
2. High beam (+)
3. City light / parking light (+)
4. Ground (–)
5. Fog light (+)
6. Unused or extra ground

US W124 harness:

• Has separate connectors for:
  • Low beam
  • High beam
  • Parking light
  • Fog light

2. Remove Old US Lights

• Unscrew and unclip the factory sealed-beam units and disconnect all wiring.
• Keep track of which wire does what — label them if needed.

3. Wire Up the Euro Lights

You have two options:

A. Use an Adapter Harness (Plug-and-play)

• Buy or build an adapter that converts the US connector to a 6-pin Euro plug.
• Example: Search for “W124 Euro headlight adapter harness”.

B. Hardwire the Euro Headlights

• Splice the US wires into the Euro plug based on the pinout.
  • Low beam wire → Euro pin 1
  • High beam wire → Euro pin 2
  • City light (small parking bulb) → Euro pin 3
  • Fog light wire (if equipped) → Euro pin 5
  • Ground wire → Euro pin 4
• Use solder + heat-shrink or crimp connectors.

(NOTE - you can just take your car wires and put them into the headlight connector!!)

 

How do I know which wire is + or - and which ones are pin 1 to 5?

 

brown = ground = -

all the other wires are +

The 6 and 4 pin sockets should have tiny numbers on them by each pin hole on the bottom side.

 

When I converted my 87 124 wagon to Bosch Euro lights, I went through the same exercise. I did the research to figure out which pins on the headlight assembly went to which bulb, got the right six-pin connectors, put the existing pins into the correct sockets, and tapped into the running light in the signal bulb socket to power the new running light in the headlights.