My 1992 300D has no boost and the tach is not functioning. Last night I replaced the RPM sensor but the problems still exist. Any ideas?

I have no tachometer functionality on my '87 300tdt. Searching for clues.
I know there is a 60$ cable/sensor wire available, but I'd prefer to test parts rather than chuck money at it.

Is there any tech on this? How would one test the cable from the flywheel to the dash?
This is an inductive sensor on the cable yes? There is a magnet or a pin(s) on the flywheel. The tach reads a wave?

Thanks in advance.

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83 300TD (need rear wiper assembly dead or alive)
84 300SD Daily driver
85 300TD almost 400k miles and driven daily.
98 E300D *sold
86 300SDL *sold and made flawless 10 hour journey to new home.

Check the OVP relay and/or it's fuse. It handles idle control, tach, ac, and abs.

No boost on a 90-93 W124 300D? I strongly recommend doing the Wastegate conversion. It'll be the best $100 you'll spend. I recently converted and am a true believer. I drank the cool aid.
Read here!!!! Wastegate actuator swap for OM602.962?

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92 300D 2.5L OM602 OBK #59

AND so is BBDC!!!

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'84 300SD sold
124.128

this might be pertinent. DIY: Tachometer Service and Repair on 1987 300D Turbo

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92 300D 2.5L OM602 OBK #59