backlighting the headlight switch icons

SRE

New member
I searched for any mention of "fixing" the headlight switch so the icons light up instead of just having a lighted bar rotating on a pitch black dashboard after dark. Didn't find anything, but I figured it out ... so maybe this will help the next victim of Mercedes' decision not to populate the circuit board. They clearly designed the switch for full lighting, and there are blank spots on the board where the other LEDs should go, but some bean counter decided to shave a fraction of a penny cost.

Odd that no one has ever posted this info. In fact, I never found instructions on removing the headlight switch panel. See attached PDF file for 16 pics.

To remove the panel holding the headlight switch, remove the screw holding the panel BELOW it and pull that panel straight out. You might want to disconnect the battery, because the next step is to remove the A Pillar cover over the air bag. Start at the top and pull toward the center of the windshield. Once it's out, three screws are revealed at the bottom of the air bag cover. You might have to pop off the speaker cover also. Only the screw closest to you holds the headlight panel, but you might need to remove the other two and lift the long dash panel. I moved too fast and didn't take notes! See photos, and let me know if I flubbed this description.

Once you have the panel holding the switch out, you'll discover that you can't reach the screws without dismantling the vent controls also attached to that panel. Don't do it! Grab a torx bit with pliers and reach in to loosen the back screw. The front screw is easy. Now that the switch is removed, use a rag and pliers to pull the knob straight off. It does not remove easily but there is no tab or screw to release it. Just pull hard. (I found I could not pry it off, because the knob is down in a hole, but perhaps someone could figure out how.)

To open the switch box, gently slide a putty knife on two sides to release the top cover from four small tabs. A pleasant surprise: this isn't a "snakes in a can" design, nothing falls out or gets lost when you remove the translucent top cover. Many posts suggest that the icons are simply painted white on black, but it's the other way. The top cover is white plastic, mostly coated black on the outside, so light shines out wherever there is no black. The fog lamp indicator (lower left) has its own LED on the circuit board. The knob is lit through an arc of clear plastic that channels light from two other LEDs. But the LEDs that were supposed to light the icons you care about the most were left off the board. You can find places that look like they were intended for LEDs, but I didn't want to mess with surface mount components and I didn't want to screw up the board.

Cheap 12V LEDs abound online, and the ones I have use heat-shrink-wrapped series resistors to limit current. There's room in the corner of the switch cover for that resistor, so drill a hole to feed the wires out and hot glue the LED at an angle so it hangs over the curved channel. Refer to the pictures if those words are confusing. You'll want to play around a bit with the exact location of your LED, in a dark room, because you need to get the light to bounce around inside to avoid hot spots or dim areas. One LED can't get it entirely uniform, but it was close enough for me. File or grind the edge of the switch back (the black ABS plastic side) to make room for the wires and the LED, then snap the halves back together. Test before re-installing, because it's hard to open it all back up again.

I routed my LED wires under the dash to the center console where the ash tray (long since removed) used to have switched accessory power *AND* an illumination circuit that is only active when the headlights are on. That makes my hack light up when the other backlighted buttons light up.

Feedback welcome.
 

Attachments

Bobnoxious

GONE FISHING
One of peeves for schizzle I noticed the night I drove her home.

Little Details Matter. LIKE BEING ABLE TO SEE THE KNOB IN THE DARK.

Great photos and write-up. THANK YOU!
 

mgmtoo

New member
Nicely done! I just thought mine was broken, so I leave the switch on Auto. What year is your van?
 

Top Bottom