The Tell-Tale Needle
The tell-tale needle can operate in one of two modes. The first is conventional where the tell-tale needle appears to be pushed by the main needle and sticks at the highest position reached. In this mode, the needle is reset by pressing the small button supplied with the tacho.
The second mode, called auto-reset, automatically resets the needle after a period of two seconds. This is a useful driving aid as it allows the driver to monitor the maximum revs reached by the engine at each gear change without having to keep his eyes on the tachometer at the very instant of the change.
After power is applied to the tacho, the tell tale needle is driven to the maximum rpm it has seen. If the tell tale is in auto-reset mode, this shows the value that a normal tell-tale would have shown. This value can be reset at any time by simply pressing the push button.
The tacho provides two separately adjustable shift light outputs. When both shift lights are lit, they flash as an additional alert. Two special LED shift lights are supplied with the tacho.
The tachometer is quartz crystal controlled and will show the rpm to an accuracy better than 1% + or - 100 rpm on the main part of the scale. The resolution and therefore the accuracy of the compressed scale is reduced in proportion.
The tacho is powered from the car’s 12 volt supply. (As the case is isolated, it can be used with positive earth cars)
The trigger can be from any reasonable source although contact breaker type require the fitting a small filter box which is supplied with every instrument. By far the best form of trigger is from a separate sensor which will not be affected by odd ignition spikes or rev. limiters that always give a false reading when reached. Call us to discuss the options....
Click for Tacho Wiring Diagram Click for Data Sheet