W124 mirror switch illumination DIY repair - PeachParts Mercedes-Benz Forum

Jeremy5848 · #1 01-12-2009, 02:16 AM

Previously it has been mentioned in this forum that the adjustment switch for the passenger-side mirror is supposed to be illuminated. I didn't know that and first checked the schematic diagram in the ETM. Sure enough, S50, the "Outside Mirror Control Switch," was shown with a lamp. Then I pulled a spare switch out of my junkbox and disassembled it. Yep, there's a tiny lamp inside, burned out, of course. Replacing that lamp is the subject of this DIY.

The lamp in question is commonly referred to as a "grain of wheat" lamp and that's about how big it is. (This is a job in which tiny fingers are really helpful.) These lamps are often used in military equipment (where they are usually 28 volts, no help). You can sometimes find them in 12 volts at surplus electronic stores and that's where I found mine.

Taking the switch apart requires several small screwdrivers because there are six plastic tabs that hold the bottom in the case. Carefully spreading the case apart will allow you to pull the bottom out. Be careful! As you can see from the first picture, the switch is full of tiny parts. In particular, the three "dumbbell" electrical contacts and the six springs would easily disappear if dropped.

With the switch apart, you can see that the bulb is soldered to the base. Using a tiny soldering iron, remove the old bulb and solder in the new one. Note which pins on the base are for the bulb. Test with 12 volts to make sure the new bulb actually works, then reassemble the switch. The base is polarized so it can't go in backwards. The white plastic thing that holds the springs and the dumbbells likewise can go in only one way or there won't be a space for the bulb. Test again and return the switch to the car. The last photo shows the switch in a dark room with the center spot illuminated. It doesn't make a big glow, just enough to allow you to find the switch in the dark.

Jeremy