Test/remove and install solenoid switch
If the solenoid switch is defective, the pinion in the starter is not pulled into engagement with the flywheel ring gear.
As a result, the starter cannot crank the engine.
This fault occurs more often than the starter motor itself being defective.
Testing with the starter installedRemove the gear, shift lever in neutral position.
Test requirement: battery fully charged.
Using a auxiliary cable, briefly bridge terminal 30 (= thick positive cable) and terminal 50 (thin cable, to the ignition switch) at the starter; the starter pinion must snap forward (click) and the starter must run. If not, unbolt the starter and test it removed.
Remove the starter and repeat the test with the starter removed using a car battery. A jump-start cable is suitable as the supply lead to terminal 50 of the starter.
If the pinion snaps forward without the starter running, have the starter motor overhauled by a workshop.

If the pinion does not snap forward, unbolt the solenoid switch and replace it.

Seal the joint - f - to the starter with a suitable sealant.
Hook the solenoid switch onto the fork lever in the starter, then bolt it on.
Bolt on the lead for the solenoid switch.
Test the starter again, as described above.
Install the starter.
Test yourself
A quick Fiat Bravo quiz: every answer comes with an explanation and a link to the manual page.