I know there's a pickup on the bell housing (though I've yet to figure out where) and that this signal is fed to the EGR computer, which then sends a signal to the tach. But what is the nature of that signal? I've measured the resistance of the sending pickup - 1.9K-ohms so I assume that's good, and I swapped out the EGR computer from my parts car, and still no tach. So I'm assuming my tach is bad, but before I go through the effort of swapping it out, I want to make sure that this is indeed going to fix my problem, so I want to devise a test to check it out. I either want to measure the output of the EGR computer, or apply a signal to the tach to mimic the EGR computer output.

BTW, I've been under the parts car looking for the tach pickup sensor, and can't figure out where it is. Looked on the left side around the oil filter (from underneath) and didn't see anything like the picture in the manual. Where on the bell housing is it?

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mjk

'84 300SD 119KMi (Liesl der Diesel)
'84 300D 326KMi when the oil left (former parts car)
'82 300SD 253KMi (new parts car)