When is solenoid bad?

The symptom of a bad solenoid includes a rapid clicking sound indicating it is receiving too little power from the car battery. This lack of power may be from a low battery or corrosion of the battery cables causing the engine to not start. Corrosion is also possible in the internal solenoid connections, or a blocked plunger may lead to the solenoid being flooded with power and burning out the internal connections to damage the unit. Clicking on attempted ignition should be a warning to have the starter system checked.