The solenoid has 4 posts, 2 small and 2 large.
The small posts are the control (coil).
Use an ohmmeter or continuity tester, it should show continuity or resistance.
The large posts are the contact points the connect the main battery power together.
Use an ohmmeter or continuity tester, it should show open or infinite resistance when no power is applied to the coil. With the coil energized (solenoid on) it should show continuity or a very small resistance.