The previous advice about the large power cable from the battery is good. The large cable DOES power the starter MOTOR; but, it doesn’t power the starter SOLENOID (which is making the “click, click, click”).
The starter solenoid is powered by a small wire from the ignition switch. Poor wire connections along the way, from the ignition switch to the starter solenoid, cause the voltage to drop by the time it gets to the starter . The dropped voltage is not enough to energise the starter solenoid; only enough to make it go “click, click, click”.
To find where the poor connections are, from the ignition switch to the starter solenoid, requires following the path of the small wire and checking its voltage at points along that path. Some “mechanics” who don’t know how, or won’t, perform these checks, use the expedient(?) of just changing parts until they get lucky.