The Oil Level Light is lit in the instrument panel after replacing the coolant level sensor on the overflow tank. Maybe I touched or washed something sensitive under the hood...? Maybe it is a bad sender? Maybe my wiring harness is kaput?

I cannot find the sender location or the wiring location, or a connector for it, and I have the Manual CD! Is it on the CD, if so where? I found the wiring diagram, but without component location it is pretty useless to me.

Please help!

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2004 E500 4Matic 138,000 miles