Just to let you know:
The symbols around the light switch of the W123 are NOT illuminated.
The symbols around the switch of the W124 ARE illuminated (or, at least, should be).
Pull off the knob of the light switch (and then you will see the fog-light indicator) and untighten the nut of the light switch. Pull the black panel (gently) towards the driver seat and after the opening passes the threaded part of the light switch, move the panel to the left (door-side) to unhook two (or three) clips at the back of the panel between switch and steering column.
The bulb is stuck in a plug at the back of the panel!
with a minor 600+k