Thanks guys for the help. I mistakenly assumed it was some sort of rheostat, which a continuous change of resistance. But because it has 7 discrete values and you need to re-engage it to determine any change, I need to go back and check it again. I also didn't realize it just popped off. So thank you.

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1968 220D, w115, /8, OM615, Automatic transmission.
My 1987 300TD wagon was sold and my 2003 W210 E320 wagon was totaled (sheds tear).