2. When connecting the tachometer to the ignition system, connect the tachometer live lead to the IG (-) terminal of the ignition module diagnostic connector and the power lead to the battery as shown in the figure.
3. Since not all tachometers are compatible with this ignition system, please make sure that the tachometer is compatible before using it.
4. Never allow the tachometer output contacts to touch the ground: this will result in failure of the switch and/or ignition coil of the engine being tested.
5. Do not disconnect the battery while the engine is running.
(The information was taken from a web portal: «Toyotaman.ru»)
6. Make sure the switch is securely connected to the vehicle ground.