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Discussion Starter · #1 ·
Where would be to best place to attach an oscilloscope to the Sensor -> Tachometer wiring to get the easiest reading? Would it be at the sensor or at the tachometer? Is it correct that the sensor is on the gear box bell housing?

It all works fine, it is just some research I am doing. Thanks for any help!
 

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Discussion Starter · #2 ·
I removed the instrument panel from the dash board yesterday and removed most of the covered until I could get to the four tachometer connections on the back. I then plugged the cabling back in and started the car. Using an oscilloscope, I put the probes on each combination of the pins and got the output.

It looks as though it accepts square wave ( or pulsing input ) that alternates between positive, neutral and negative ( seems to only be between positive and neutral when idling ) , the frequency of which increases as RPM increases. This was true on several combinations. Does that mean my tachometer is a stepper motor?
 

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You get bonus marks for doing this. Connecting a scope to the tachometer sensors was always something I wanted to do with my 405 but never seemed to find the time. The 405 has since been passed on.

If the tachometer was a stepper motor then the tachometer would just rotate. Depending the duty cycle of the pulses at different speeds I would have expected a very simple frequency to voltage converter and a basic voltage meter arrangement - as would be the case on most analogue instruments. I could be wrong.

While you have the car apart - do a quick bit of reverse engineering to work out what electronics there is associated with the tachometer.
 
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