Wiring a rev counter to alternator?

Paul Posted a lot Posts: 1,907	Wiring a rev counter to alternator?Paul @lard44
	Feb 2, 2021 14:27:41 GMT Select Post Deselect Post Link to Post Back to Top
	Hi all, I'd like to connect a rev counter to my diesel taxi - 2.4 Duratorq, same as mk6/mk7 transit. Alternator only has 3 wires + earth as below...which one do I take a spur from? Or are none of them appropriate? Obviously not B+, and if 1 is the warning light on the 'instrument pack' (that's where it's headed) the my guess would have been number 3...?


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xbl Posted a lot Posts: 1,354	Wiring a rev counter to alternator?xbl @xbl
	Feb 2, 2021 15:00:21 GMT Select Post Deselect Post Link to Post Back to Top
	The tach on the MK6 and 7 tranny runs from the PCM. Check if your alternator has a W terminal, this is usually A/C to provide a calibrated tach with it's signal.


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squonk Part of things Posts: 857	Wiring a rev counter to alternator?squonk @squonk
	Feb 6, 2021 11:36:16 GMT Select Post Deselect Post Link to Post Back to Top
	The W terminal is taken from the unrectified side of the diode pack so it gives an ac signal. If an alternator doesent have this terminal it is relatively easy to add a cable soldered to the correct side of the diode pack (ac input). An autoelectrician should be able to do this for you relatively cheaply. You may also find that if the tacho isn't designed to run on an alternator signal it might not work. Those that run from the coil take a 0 - 12v dc pulse whereas those designed to run from a W terminal take a +/- 12v sine wave signal.
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