Maybe he means that the different models (E-class vs S-class) have different electrical properties in the fuel–temp–pressure sections of that 4-gauge panel? My swap was 300E to 300D so there was no problem; the only S-class component in mine is the faceplate, to eliminate the unleaded premium labeling that came with the 300E.

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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