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Tachometer problem

James Devereux

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Hi All, 


I have recently swopped out my old electronic distribution unit that I believe was an old Sierra one for a Bestek one. 


Everything is working great but now the tachometer does not give a reading. There were a few additional wires that were going into the old plug so I don't know if disconnecting those has caused the issue. 


Any ideas how to solve this or where to start?



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In the original Sierra systems the pulsed input feed needed by the tachometer is a green wire that connects to the low tension (12v) connector on the coil. On the coil, apart from the thick HT lead going to the distrubutor, there should be a single (normally black) wire that comes from the ignition switch. The other connector would have two wires connected (normally green), one of which goes to whatever ECU you are using, and the other to the tachometer. When the ignition is on the the green wires should be live. The tachometer will have 3 connectors, one to earth, one to a constant 12v (with the ignition on), one with the pulsed feed from the ignition coil (probably green). So you need to get out a volt meter and check the wires that have not been connected, or visually look for the one from the ignition coil (probably green) that is probably not connected to the tachometer.


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