What ignition system did the Ford Model T use?

The Ford Model T used a magneto ignition system.

Its unusual low-voltage magneto was built into the engine’s flywheel. As the flywheel rotated, the magneto generated alternating current, which was sent to the trembler coils that produced the high-voltage pulses needed to fire the spark plugs. This arrangement was distinctive among automobiles of the period.

The magneto helped the Model T operate without a conventional starting battery, so a correctly performed hand-crank could generate the electricity needed to start the engine. That is why “magneto” is the canonical answer, even though the complete system also included coils and spark plugs. Electric lighting appeared in 1915, while an electric starter arrived later, becoming available from 1919 and more broadly fitted during the 1920s.