The switch knob itself is not illuminated, apart from the central indicator for the rear fog light, which comes on when the switch is pulled out to the second detent position. The indicators around the switch knob are lit from behind, so either the bulb has blown or the bulb holder is unclipped.

Pull the knob, undo the big nut holding the unit in place and pull the unit out to check. Be careful when you unlip the plastic panel from the dash, it's clipped in and the plastic tongues break easily. The bulb holder clips into the back of the switch unit. If you have vacuum adjustment for headlight level, watch out you don't lose the hoses when you pull the unit out, the job can escalate from something simple to pull the dash nightmare if you are not careful.

You'll probably find the switch comes off in your hand when you try to pull it out to activate the rear fog. If so, you can get some relief by prising the two prongs of the switch unit apart slightly.

good luck

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1987 300e manual 250,000 km (sold)