1980 300SD w116 model.

I've tried 3 different tachs and 2 different sending units on this one. All of those parts functioned in other cars. The tachometer registers at idle (not accurate, though), maybe 200 to 300 rpm. Higher than idle it drops to zero.

At idle, turning a turn signal on causes the tach to jump up and down.

I get volts at the back of the instrument cluster: 12 to 14 or so, but tach dosen't register above idle.

Everything else works on the cluster.

Anyone run across this on before?

Any ideas?

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