Why clicking, not cranking
A rapid click is the starter solenoid trying — and failing — to pull in, because it isn’t getting enough current.
Rapid clicking when you turn the key almost always traces back to the battery or its connections.
Rapid clicking, not a single click
Dashboard lights come on but dim
Classic signature of a starter not getting enough current.
A jump-start confirming the car runs fine afterward is a strong sign.
Crust on the terminals raises resistance enough to cause the same clicking.
A wire brush and a $6 cleaner kit often fixes this in 5 minutes.
Less likely with dim lights, worth ruling out once the battery tests fine.
A rapid click is the starter solenoid trying — and failing — to pull in, because it isn’t getting enough current.