When replacing electrical components, it is very important to ensure the component is properly grounded. Do not overlook the importance of the ground wire. Although many times an ungrounded component will not affect the operation, it is not safe.
If a bare section of electrical wiring within a component, such as the winding of a motor, touches its casing, the ground wire will allow the current to flow safely to an earth ground. This will typically cause the overcurrent protection device (fuse or circuit breaker) to shut down the system. This prevents further damage to the system or anyone servicing it.