I am not real familiar with imports, and there may be a solenoid on the alternator, I have never seen one.
The solenoid is usually on or associated with the starter. The solenoid would basically be a large actuator and/or relay for switching the huge amount of current required for the starter. Usually mounted on the starter itself, some are mounted on a fender well or firewall. Easy to find, just follow the largest + positive lead from the battery and the solenoid should be the first thing that cable goes to.