hello gents,

My tach doesn't work. I already swapped tach amps, with a verified good one, and tried the old cigarette butt trick, to no avail. I inspected teh actual tach, and no connections look broken, cold, or burned. has anyone seen anything else that will cause a tach not to work? It never moves.

The sensor could have 20 years of gunk on it,even though it's a magnetic pickup it works better if its clean.When I bought my car (1983 300SD) the tach did not work, looked as if someone used a pry bar when adjusting the belts and bent the sensor bracket 45 degrees,the sensor did not have anything to pickup,I fixed the sensor bracket,cleaned the sensor,did a modified cigarette butt trick useing a fiberglass spacer and my tach has worked ever since.

I know on my 300D, the seat belt light will turn on and off. From time to time the glow light will also flicker on while the seatbelt light is on. When this happens, the tachometer also dips way down. Does your glow plug light work? Is the cluster properly grounded? Maybe a bad ground will do this???

Good luck,

JMH

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Current Diesels:
1981 240D (73K)
1982 300CD (169k)
1985 190D (169k)
1991 350SD (116k)
1991 350SD (206k)
1991 300D (228k)
2008 ML320 CDI (199k)
1996 Dodge Ram CTD (442k)
1996 Dodge Ram CTD (267k)

Past Diesels:
1983 300D (228K), 1985 300D (233K), 1993 300D 2.5T (338k), 1993 300SD (291k)

There's also a relay under the dash on the passenger's side. This has effect on the tach operation and also the A/C compressor.

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Regards,
Aaron