Yes, by far most tachometers work in combination with a 123ignition.

A standard voltage-triggered tachometer should be connected as follows:

To make RVI-type tachometers, manufactured by Smiths Company, work correctly, the distributor must be connected differently. The red wire must be connected to the switched positive from the ignition switch instead of to the ignition coil.

The reason: the current flowing through the ignition coil to create a spark is measured by the RVI tachometer. It is the current used by the computer inside the 123ignition that passes through the tachometer and causes an incorrect reading.

Solution: the current required to operate the computer inside the 123ignition will no longer pass through the tachometer if you connect the red (positive) wire of the 123ignition directly to a switched positive supply.

See the wiring diagram for the negative ground version below:

Below is the wiring diagram for positive ground:

How: you can find this switched positive using a test lamp by checking, for example, the fuses while switching the ignition on and off.

If you have another type of tachometer that behaves erratically, it is best to install a diode (1N4007) in series with the tachometer. Note: the striped end of the diode must point towards the tachometer.