The tach is NOT cable driven on a 300DT.
The tach gets its signal from the pickup at the harmonic balancer. The grey
harness goes up to the
diagnostic plug on the inner left fender. The cap is a electronic circuit board
that converts the
A/C signal to the signal the tach understands. Unscrew the cap, remove it, look
at the pins,
reinstall the cap. It may start working right.....
It was a very poor system. In the 84 year models and up, MB got smart and put
the tach pickup on the
flywheel. Much better system.
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