18 hp twin cylinder

I have a question for who ever has an answer, I have a 18 hp magnum twin cylinder on a gt 18 ariens my problem is I have a wire coming from the starter to the solenoid, on the other side of the solenoid wire goes to the battery, there is one small wire at the bottom of the solenoid, when I turn my key to the start nothing happens motor wont turn over, is there another wire i need thank you.

18 hp twin cylinder