Tach Rebuild


The conversion of the distributor to a Pertronix ignition system requires an upgrade of the Smiths tachometer.  The Lotus comes with a RVI tach that will not work with the Pertronix system.  SPIYDA Design has created a circuit board that fits into the current housing and makes it a RVC type tach.  The process is not complex if you know how to solder and have the courage to cut the original wires and modify the connections.  The photo shows the original wiring of the tach before the installation.

The main wires that will change are the white wires which are removed from the tach and connected together.  One has a male connector and the other a female so they will easily connect.  That circuit was the timing trigger for the tach and also supplied 12 volts to the coil.  The new circuit board will replace that part.  The connector with the two green wires remains where it is.


Here’s a photo of the parts inside the tach.  The original part is on the bottom left and the new board is just above it.  You need to cut a few wires to get to this stage.


The new board fits cleanly into the housing.

You will need to run a new White wire from this board to the coil.  That wire serves as the new trigger for the tach.  That’s only new wire you will need to run.  Calibration was simple with the supplied support wire and sound file.  The instructions are great and the system worked as advertised.

And, it now works.

© Donald Shikoski 2011