What is indicated by a magneto timing light?

A magneto timing light is a specialized tool used during the ignition timing process of an engine. Its primary function is to indicate the precise moment when the magneto points open, which is critical for ensuring the correct timing of spark generation in the ignition system. This timing needs to be accurately set to optimize engine performance and prevent issues such as pre-ignition or misfiring.

When the magneto points open, it allows the current to flow to the ignition coil, generating a high-voltage spark that ignites the fuel-air mixture in the engine's cylinders. By visually indicating this moment, the magneto timing light helps mechanics and technicians ensure that timing is set accurately according to the manufacturer's specifications, which can significantly affect engine efficiency and performance.

The other options do not pertain to the function of a magneto timing light; it does not measure engine temperature, assess fuel efficiency, or quantify the amount of spark produced. Instead, it strictly serves to show when the magneto points open, which is a critical element for setting up the ignition system correctly.