if its like the diesels there should be a little "trash can" looking plug on the wheel well that commonly comes loose.

check this url. www (dot) benz world (dot) org/forums/w123-e-ce-d-cd-td/1597328-w123-300td-tachometer-problem.html

i chopped up the url a little. im not sure if im supposed to post links to other sites.

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Drank got me lazy
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