I know what you mean about all the different tachs, I've bought a few tachs over the years trying to get them to work. I also found that some outboard tachs with the adjustable poles, 2,4,6,8,12, etc were made to run on 12V DC and not 12V AC.I think you can usually figure out the pulse by dividing the number of magnets in the flywheel by two, but on some engines the number of magnets was the same as the pulse of the tach.
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