In order for your engine to turn, all parts of the ignition system have to work cohesively. When a solenoid is stuck open or closed it will result in starter problems.
As an integral part of any vehicle's ignition system, the solenoid, or starter, relay is a magnetic switch that actuates the starter motor in order to turn the engine.
If you engage the ignition switch and the engine does not turn but instead emits a repetitive clicking sound, your solenoid is stuck open or closed and will need to be replaced. In some cases the damage can be extensive, requiring a complete overhaul of the starter. Due to its position in the engine compartment, the replacement of your defective solenoid should be performed by a certified technician.
Your solenoid is connected to the positive battery cable and can easily be corroded by battery acid or other engine fluids. It's wise to check regularly to ensure that these terminal cables are clean, and to immediately replace cables that are damaged.