If you are fitting an RVC tachometer where there was previously an RVI
ignore the old signal wire and run a new wire from the coil / ecu / electronic ignition as appropriate
(if the old signal wire (usually white) connected to the tacho with a male and female bullet connector, connect them to each other.
When converting to an electronic ignition, add a new power feed from the ignition switch or fuse box. This will minimise interference generated by the coil.
If you power the electronic ignition or tachometer from the terminal on the coil, unpredicatable results (usually bad) may occur.
RVI Tachometer with Coil and Points
The Smiths RVI tachometer has either an internal or external pick up coil.
The feed to the ignition coil (often a white wire) is looped around the pick up coil.
When the points close, electricity passes through the coil to ground. As the electricity passes through the loop on the tacho
a current is induced in the tachometer pick-up coil. This current is filtered and processed and used to drive the moving coil movement.
RVC Tachometer with coil and points
An RVC tachometer does not have the pick-up coil, rather its electronics are connected directly to the switched side of the coil.
The tachometer senses the voltage increasing in the primary winding of the coil when the points close.
Voltages in this circuit can be as high as 600V due to the effect of the collapsing magnetic field when the points open
On our conversion boards this wire should be connected to the pad furthest from the chip (this will be clear in the instructions),
When fitting an RVC tachometer in place of an RVI, a new wire "X" will need running from the coil -ve termional to the Signal Input "S" on the tachometer.
RVC tachometer with "Tacho Out" Electronic Ignition
The simplest wiring is when an electronic ignition system provides a "Tacho Out" signal.
Our conversion board (version "e") should should be fitted with the pad second nearest to the chip connected to the "tacho Out" of the ECU or electronic ignition