What causes the crank relay coil to de-energize, thus de-energizing the starter solenoid?

The de-energization of the crank relay coil, which in turn de-energizes the starter solenoid, is primarily caused by the opening of the speed switch. This switch is designed to detect when the engine has reached a specified operational speed, signaling that the engine is running effectively. When the speed switch opens at this threshold, the electrical circuit to the crank relay coil is interrupted, leading to the deactivation of the starter solenoid. This is a critical safety feature that prevents the starter from engaging while the engine is already running, thus protecting the engine and the starter system from potential damage.

In this context, battery failure would lead to a lack of power to the entire starting system, but it does not specifically affect the crank relay’s operation regarding de-energization through the speed switch. Overheating might occur due to various electrical component failures but is not directly related to the crank relay's operation mechanics concerning de-energization. Similarly, while fuel pump operation is essential for engine functionality, it does not impact the operation of the crank relay or the starter solenoid in this context.