On a Mercedes, there are four different circuits for the headlights. L/R and Hi/Low. Fogs usually run off on the four fuses.

Since one fog works and the other does not, sounds like you disturbed the wiring/connection.

Disclaimer: I've never worked on a W140.

Jim

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14 E250 BlueTEC black. 45k miles
95 E320 Cabriolet Emerald green 66k miles
94 E320 Cabriolet Emerald green 152k miles
85 300TD 4 spd man, euro bumpers and lights, 15" Pentas dark blue 274k miles