No difference between the W115 and the W114 instrument clusters, except for the speedometer, which varies by engine.

I've had many apart, and I do not recall any relationship between the fuel gage and the dimmer.

I suspect coincidence or ground.

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