Re: Tachometer

Posted by HH56 On 2018/2/14 16:00:42

Keith's idea may work but for that approach you need a tach with two power wires and not the typical 1 wire with the case providing the other connection. It also needs an inductive sensing rather than a direct connection to a coil lead and an incandescent bulb for the dial. If you have one with separate wires verify neither of the pos and neg power are directly connected to the case or else make very sure that the tach mounting and case is isolated from dash metal when it is mounted. If a power wire is common to the case and was hooked up to an opposite polarity battery connection then you would have a direct short when the case was mounted and it touched a regular ground.

If you do not have a dual power wire unit but still one with an inductive sense it may still be able to be used by mounting the tach in a plastic housing attached to the dash. With the tach isolated from a regular grounded surface run a wire to the tach case and connect that to a switched source and use the regular power lead to connect to ground.. Modern units with an incandescent bulb illuminating the dial should work but one with an LED may not since there is probably no way to change the LED or isolate it from the rest of the circuitry.