I have a 1982 300CD US with a non functioning Tachometer and clock. Are there common causes for this failure?

Failed capacitors on the clock, tach amp for the tach (search this forum).

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Poor fuse connections on both.
Capacitors in clock and tach amplifier have dried out.

Broken traces in circuit board of tach amplifier.
Poor connection in female plug of diagnostic port where the tach amplifier plugs in.
Hall effect sensor incorrectly adjusted (too far from trigger on crankshaft).

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If they both stopped functioning at the same time is one scenario. If they did not is the other. If you do not know they both failed at the same time. You pretty much have to assume it was not a supply voltage loss. Or grounding issue.

Good to see this. Coincidentally my newly acquired '84 300D has the same issue.

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1986 300SDL, 362K
1984 300D, 138K

Like Barry12345 said. If they both quit at the same time it is most likely a power or grounding issue. If they quit at different times, then it is most likely capacitors in the clock. The tach could be as simple at the cigarette butt trick in the tach amp, all the way up to a bad tach head unit. Do a search on clock repair and the cigarette butt trick for the tach amp. Both are relatively easy fixes.

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