The I terminal was discontinued in 1980, as this circut was placed into the ignition switch wiring instead.

The factory installed solenoids will not have an I terminal, 1980-1986, but the replacement Motorcraft ones will have a I terminal, because it can be used on a plethera of different year models, cars and trucks.

The difference in starter solenoids depended on Engine size, and charging system (IE: Battery cranking amps).

The Smaller style in post three was used with the smaller engines with lower cranking amps required.

The style in post one was for the larger engines, or with optional batteries and/charging systems that had higher cranking amps.

You can swap the "post three" type, with the one pictured in post one, but wouldn't do it the other way around.

 

The I terminal is handy for a practical joke. Runn a jumper from it to the horn relay and everytime the unsuspecting trys to crank the truck the horn will blow. Its a freaking hoot.

 

Please dont give me fun ideas like that, all my friends are going to need underwear now.