When replacing a three terminal starter solenoid with a 4 terminal on a 1987 Ford Ranger 2.91 how do you hook it up so it will not drain the battery?

One small terminal is labeled "S" and that is hooked up as before. The 4th small terminal is labeled "I". Leave alone as if it was not there. It goes to ignition coils on some cars, but if you did not have that before leave it disconnected. The other two large terminals are the same. George