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Message: <blockquote data-quote="kilohertz" data-source="post: 103557" data-attributes="member: 6974"><p>SUCCESS! I took my portable scope outside and connected to the flywheel RPM sensor (2 wires only) and it generates a nice clean sine wave, at twice the RPM so there must be 2 magnets in there, it was reading 2 KHz which is twice the actual RPM of 1000, confirmed with my model airplane optical tach, I painted a white blotch on the flywheel and it read 1000 RPM (idle). Then did some more research and found that some newer alternators have a P or W terminal on the back, which can be used to supply a signal to a tach, it connects to the diode stack internally and provides pulses. I measured 230 Hz on mine at idle, which when converted to single pulse per revolution is 13,800 RPM, but then most automotive tachs are designed to read correctly based on 4 pulses per rev on an 8 cylinder, 3 on a 6 and 2 on a 4 cylinder engine. I connected my tach to this terminal and it worked, but it read 3,500 RPM when set for an 8 cylinder engine. I took the tach apart and found there are 3 resistors, one for each of the 3 switch positions, that correspond to 4, 6 and 8 cylinders, measured them, did a bit of math and changed the one resistor that was 35K for the 8 cylinder to a 6K and it now reads perfectly, 1,000 RPM, confirmed with the scope on the flywheel sensor all the way up to 3,000 RPM. Yeah! Mounted it below the gauge pod and it looks great, even has a backlight. Hope this helps anyone who wants to add a tach to their Diesel engine. Cheers</p></blockquote><p></p>

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