That clicking noise is your starter solenoid. There can be different causes, the most common is the battery. I will explain what is happening.
Your starter needs a lot
of power to turn your engine. That much power
would melt your ignition switch in no time if it passed directly through
it. So what happens instead is your ignition switch actuates another
electric switch called a solenoid. The solenoid is a
really HEAVY DUTY switch.
it are two copper contacts that look like the head of a bolt only
rounded. The battery is attached
to one, the starter to the other.
Hovering above them on a spring is a copper clad disk attached to an
iron core. The iron core is inside an electro-magnet.
turn your key (in a perfect world), an electromagnet is activated that
yanks the disk towards the contacts (Making a single decisive healthy
CLICK). When they connect, the circuit
closed and the starter turns over. OK.
When things go wrong:
- The solenoid requires power to actuate.
- The starter takes a lot more power to turn the engine.
- When the battery is low, there isn't enough power to do
- You turn the key, solenoid engages (CLICK)
- Power goes to the starter
- The starter tries to turn the engine
- The draw from the starter drops the available power
below the minimum needed to keep the solenoid engaged.
- The solenoid disengages
- The starter is no longer drawing power
- The additional power allows the solenoid to re-engage
- Repeat the process for as long as you have the key
That's where those clicks are
coming from and why.
Short term - Jump start
term - Charge or replace battery.
There can also be a problem with the solenoid. Specifically, with that copper clad disk I mentioned earlier.
When that many amps are drawn from a battery there is heat and sparking which erode the copper plating. There comes a point where ther disk can no longer 'Complete the circuit'. It then needs replacement.
How to tell the difference?
If it's the battery, a jump start will work.
If it's the solenoid, a jump start will have no effect.
I wanted to explain what
was happening rather than just saying 'dead battery, replace it'. That
way you can judge for yourself whats going on.
I hope you can find the time to rate this response.