There is usually a neutral safety switch to keep the motor from starting in gear. If your ignition key is on the dashboard, then there will be one or two wires from it to the control. Those go to the neutral safety switch.
If the wires are good, you probably need to take the control apart to get at the switch.
Side panel mounted control, right? The throttle arm and cover plate usually come off the outside of the control, and it then can fall down under the side panel. Look for an allen set screw in the throttle arm. You may need to put the boat is full reverse to get to it.