What causes the crank relay coil to de-energize, thereby causing the starter solenoid to de-energize?

The crank relay coil de-energizes when the speed switch opens, which is essential in starting engine operations. The speed switch is designed to monitor the engine's rotational speed. During engine cranking, the speed switch remains closed, allowing current to flow through the relay coil, which in turn energizes the starter solenoid. Once the engine reaches a predetermined speed, the switch opens, cutting off the power to the crank relay coil. This de-energization stops the operation of the starter solenoid, effectively disengaging the starter motor from the engine, preventing potential damage from continuous cranking after the engine is started.

While voltage drop, temperature change, and battery discharge can affect various components in an electrical system, they do not directly cause the crank relay's de-energization in the context of this question. It is specifically the action of the speed switch opening that is responsible for this transition, making it the correct answer.