Changing the auxiliary indicator — also known as the side marker light or corner light — on your Mercedes-Benz W201 is a straightforward task that can be done with basic tools. Follow this step-by-step guide to replace it safely and correctly.

Tools and Materials Required

• Replacement auxiliary indicator (correct side and model for W201)
• Screwdriver (Phillips or flathead, depending on screw type)
• Socket set (optional for some versions)
• Protective gloves
• Safety glasses

1. Safety Precautions

• Park your vehicle on a level surface.
• Turn off the engine and engage the handbrake.
• Wear protective gloves and safety glasses to avoid injury.
• Ensure the vehicle lights are switched off before working.

2. Locate the Auxiliary Indicator

• The auxiliary indicator on the Mercedes W201 is typically located on the front fender, beside the headlight or near the wheel arch.
• Identify which side (left or right) needs replacement before proceeding.

3. Access the Indicator Housing

Depending on your model configuration:

• You may access the light from inside the engine bay, behind the headlight assembly.
• Alternatively, remove the inner fender liner or access it through the wheel well for better reach.
• Use care to avoid scratching the fender paint.

4. Remove the Indicator Housing

• Locate the screw(s) or bolt(s) securing the indicator housing.
• Use the appropriate screwdriver or socket to loosen and remove them.
• Carefully pull the indicator housing forward — avoid pulling hard, as the wiring is still connected.

5. Disconnect the Wiring Harness

• Locate the wiring connector at the back of the housing.
• Press the retaining tab or gently pry it with a small flathead screwdriver.
• Pull the connector straight out to disconnect the old indicator.
• Set the housing down gently to prevent lens damage.

6. Remove the Old Indicator

• If the indicator lens is clipped in, press the locking tabs to release it.
• Slide or lift the old indicator out of the housing carefully.
• Inspect the socket and wiring for dirt or corrosion; clean if necessary.

7. Install the New Auxiliary Indicator

• Align the new indicator lens or assembly with the housing.
• Snap or slide it into place until it locks securely.
• Confirm it sits flush with the fender and has no visible gaps.

8. Reconnect the Wiring

• Plug the wiring harness connector into the new indicator’s socket.
• Push until you feel or hear a click, ensuring a firm connection.
• Double-check that the connector is not loose or misaligned.

9. Reinstall the Indicator Housing

• Position the indicator housing back into its original location.
• Insert and tighten the screws or bolts that were removed earlier.
• Ensure the assembly is secure and properly aligned.

10. Test the New Indicator

• Turn on your vehicle’s lights and check the side marker illumination.
• Activate the turn signal to confirm the indicator blinks correctly.
• If it does not work, check the bulb, connector, or fuse.

11. Adjust and Finalize

• Adjust the indicator’s position if it appears misaligned or loose.
• Ensure the light beam or reflection is even and visible.
• Wipe the lens surface clean of fingerprints or smudges.

12. Final Inspection

Perform a quick final check:

• The indicator is securely fitted
• The wiring is firmly connected
• The light functions correctly (steady and flashing modes)
• There are no gaps, rattles, or exposed edges

Troubleshooting Tips

Summary

Replacing the auxiliary indicator on a Mercedes W201 involves removing the old light, connecting the new one, and ensuring proper alignment and functionality. The process typically takes 15–30 minutes and can be performed with basic tools.