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Tacho connection

John Appel

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I have a Link G4 Storm on a twin cylinder motorcycle engine. I want to fit a tacho driven by the tacho function . What is the difference between a high level and a low level tacho. I am looking at a Prosport 80mm tacho which has a stepper motor movement. The model I am looking at comes in either a petrol or diesel application. The petrol one goes up to 10,000 rpm and the diesel one goes up to 8,000 rpm. The two look identical apart from speed range. I prefer the diesel one because of the lower full scale reading. I have copies of the data sheets for both these tachos and the wiring terminals on both are the same. The input is marked "connector for sensor wire". For the petrol model it is shown going to the ECU. For the diesel model it is shown going to the alternator. Would the Link ECU drive the diesel model. Any ideas anyone. Regards, John

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Hi John, 

The low level tacho output on a Link ECU means that the signal is 0 to 12 volts with the ECU pulling the signal to ground. My understanding is that many of the old tachos that used the coil negative actually used the rising voltage after the points opened to drive the tacho.

Just about all aftermarket tachos now use a low level signal as provided by the Link ECUs. There are diagrams on the internet for converting a high level tacho to use a low level signal. Here is one:


The best bet would be to confirm the operation with the tacho manufacturer.

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