It depends on your model, but 1984 and up do not have an amp. There are lots of articles on the "cigarette butt" trick and such.

Only applicable to the pre 1984s (at least on the 123 chasis, probably on the 126 chasis also).

My intermittant tach probs are similar to yours, and in my case are due to a dirty/malfunctioning/poorly attached pickup.

best of luck (but it would help to know the model and year of your car).

alec

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84 300TD - 235k - Farbe "Surfblau" bought at 213k
87 300SDL - 131k - Farbe "PimpGold" bought at 115k
00 Klepper Faltboot Expedition Double