What is the reason why a motorcycle cannot be turned off with the key?

[Riley]

If it is an AC ignition motorcycle, the inability to turn off the engine with the key is due to poor contact of the key switch or detachment of the kill wire. If it is a DC ignition motorcycle, the key switch is damaged and cannot cut off the power when turned off. Below are the relevant explanations: Relay damage: If "cannot be turned off" means the engine stops after turning off and removing the key but continues to rotate under the drive of the starter motor, the starter relay is damaged. First, tap on the relay casing, then disconnect the battery, starter motor, or relay wiring, and finally replace the relay. Introduction to relays: A relay is a control device that establishes an interactive relationship between the control system (also known as the input circuit) and the controlled system (also known as the output circuit). It is commonly used in automated control circuits, essentially functioning as an "automatic switch" that uses a small current to control the operation of a large current. Therefore, it plays roles in automatic regulation, safety protection, and circuit switching within the circuit.