Is that(potentiometer) the rheostat/dimmer switch??
If so, I have done it. No difference in brightness, the 1986 and 1987 300E are known for their dim dashes.
1987 mercedes 300E
1995 e320 conversion(hated the 300e grill)
Monochromatic Paint (Custom Blue)
Flat Badged (front)
custom "carbon fiber" console
18 inch HP EVO rims
Sold! Now I drive a Monte Carlo SS