"Stand alone" type, 3 terminal starter solenoid used in various Indmar applications.  The actual solenoid sent may be a 4 terminal design (part # 755005) which is also designed to work in a 3 terminal application.

Connections for 4 terminal design in a 3 terminal application is as follow: 

1 larger terminal is connected to the battery lead 

1 larger terminal is connected to the starter lead   

Smaller 3rd wire is connected to terminal marked on solenoid as "S" for the switch. 

The 4th terminal marked "I" is left unconnected.