Dimmer Switch

Replace the headlight dimmer switch (multi-function switch) on the steering column, which controls high/low beam operation and turn signals.

Warnings

Tools required

Parts

• Dimmer/Multi-function switch assembly × 1 — A 221 540 XX XX (Mercedes-Benz OEM)
• Steering column trim clips (if damaged) × 4 — Use OEM specification

Preparation

1. Park vehicle on level surface and apply parking brake
2. Turn steering wheel to straight-ahead position and lock ignition
3. Disconnect battery negative terminal and wait minimum 15 minutes for airbag system discharge
4. Adjust steering column to lowest and fully extended position for access
5. Ensure adequate lighting in footwell and steering column area

Procedure

1. 1

   Remove lower steering column covers
   Remove the lower steering column trim cover by carefully prying out the trim clips on both sides. Remove the T20 Torx screws securing the lower cover (typically 3 screws). Gently pull the lower cover away from the column and set aside.
2. 2

   Remove upper steering column cover
   Locate and remove the T25 Torx screws securing the upper steering column cover (typically 2-3 screws). Carefully separate the upper cover from the column, being mindful of any wiring harness clips attached to the cover. Disconnect any courtesy light connectors if present.
   Torque spec

   Cover Screws15 Nm (11 lb-ft)
3. 3

   Access dimmer switch module
   With column covers removed, identify the multi-function switch assembly on the left side of the steering column. Note the position of all connectors and wiring routing. Take a photo for reference during reassembly.
4. 4

   Disconnect switch electrical connectors
   Locate the primary electrical connector on the back of the multi-function switch. Press the release tab (typically red or gray) and carefully pull the connector straight back. If equipped with multiple connectors for wiper/cruise functions, disconnect all connectors from the switch assembly.
5. 5

   Remove switch mounting hardware
   Locate the module mounting bolts securing the multi-function switch to the steering column (typically 2 bolts, T25 or T30 Torx). Support the switch with one hand while removing the bolts. Note the exact position and orientation of the switch for installation of the new unit.
   Torque spec

   Module Mounting Bolts8 Nm (6 lb-ft)
6. 6

   Remove dimmer switch assembly
   Carefully slide the multi-function switch assembly off the steering column shaft. Avoid contact with the clock spring assembly behind the steering wheel. Inspect the column for any damaged wiring or loose components before installing the new switch.
7. 7

   Install new dimmer switch
   Position the new multi-function switch onto the steering column in the exact orientation noted during removal. Ensure the switch actuator properly engages with the column mechanism and that all mounting holes align correctly. Verify the switch moves freely through all positions before securing.
8. 8

   Secure switch mounting bolts
   Install the module mounting bolts finger-tight first to ensure proper alignment. Using a torque wrench, tighten the mounting bolts to specification in a cross pattern to ensure even seating of the switch assembly.
   Torque spec

   Module Mounting Bolts8 Nm (6 lb-ft)
9. 9

   Reconnect electrical connectors
   Reconnect all electrical connectors to the new switch assembly, ensuring each connector clicks firmly into place. Verify the locking tabs are fully engaged. Route all wiring as originally positioned to avoid pinching during cover installation.
10. 10

    Reinstall steering column covers
    Position the upper steering column cover and install the cover screws, torquing to specification. Reconnect any courtesy light connectors. Install the lower cover and secure with T20 Torx screws and trim clips. Ensure all panels fit flush with no gaps.
    Torque spec

    Cover Screws15 Nm (11 lb-ft)
11. 11

    Reconnect battery and initialize system
    Reconnect the battery negative terminal and torque to specification. Turn ignition to position 2 (do not start engine). Cycle the dimmer switch through all positions several times. Check instrument cluster for any warning lights related to lighting or switch malfunction.
    Torque spec

    Battery Terminal Bolts6 Nm (4 lb-ft)

Reassembly

1. Verify all steering column trim panels are properly seated and secured
2. Confirm all electrical connectors are fully engaged with locking tabs seated
3. Check that no wiring is pinched between column covers
4. Ensure steering column adjustments still function properly after reassembly

Verification

• Test headlight dimmer function: high beam and low beam should toggle properly with switch movement
• Verify turn signal operation in both left and right positions with proper cancellation
• Check that high beam indicator illuminates on instrument cluster when activated
• Confirm no warning lights or error messages appear on instrument cluster
• Test all secondary functions: turn signal lane change tap, flash-to-pass operation
• Verify proper switch return to center position after turn signal use
• Use Mercedes-Benz Star Diagnostic System to clear any stored fault codes if warning lights persist

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