| Electronic tachometers give erratic readings when their base voltage is low, usually caused by a loose or corroded electrical connection.
Usual suspects:
Most likely - Intermittent power or earth connection
Next likely - Intermittent rpm signal connection
Least likely - Tachometer internal problems
Since the bike is running OK, the RPM sensor gap, the sensor itself, and wiring back to the computer are not the problem. So, you need to check all the connectors between the computer and the tach. Check for a loose or corroded electrical connection at the battery, the fuse, and any in-line connector. Remove, clean and tighten the two battery connections first, next the connector at the instrument cluster, then at the fuse, and lastly at the wiring harness connections.
If you fail to find a problem, try to borrow a tach to verify that it’s actually the problem, before buying a replacement. |