Well, since we got a dialog going, I might as well stir it up. You are all wrong (sort of). The tach works off a prepared signal made in the ignition controller. There are no rpm or cylinder ID sensors on the crank for engine performance (whoever said it was a test sensor was right).

The ignition is phased by the pulse generator built into the base of the distributor on all M110 distributors after they got rid of points in 1977.

__________________
Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician