I have found that a pair of pliers is necessary to get a good enough grip on the knob. Pad the jaws if you wish. The orange dot in the center illuminates for the rear fog lamp (European cars only). Your switch probably does not have a bulb in it and may also be missing the contacts and wiring for the rear fog lamp. I don't think my '85 300D-T had them.

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"Buster" in the '95

Our all-Diesel family
1996 E300D (W210) . .338,000 miles Wife's car
2005 E320 CDI . . 113,000 miles My car
Santa Rosa population 176,762 (2022)
Total. . . . . . . . . . . . 627,762
"Oh lord won't you buy me a Mercedes Benz."
-- Janis Joplin, October 1, 1970