The small wire is what trips the solenoid.
The solenoid has a large gauge wire to the positive terminal of the battery, another fairly large conductor that goes from the solenoid to the starter, and the small wire.
When you apply ~12V to the small conductor on the solenoid, it "trips" the solenoid. One of the solenoid's functions is to connect the battery terminal to the starter, providing a path that allows a very high current to flow, enabling the starter motor to turn.
So if the engine cranked when you connected a 12V source to that small terminal, you demonstrated that the starter
and solenoid are good, and that 12V is probably not getting to the switch terminal on the solenoid.
Put a multimeter on that small terminal and turn the key. I believe you should see 12V when the key is turned to the start position.
If not, then something is wrong in the circuit from the keyswitch to the starter.
TB
Electricity is not tough, just think of it as plumbing that can kill
