Positive Battery cable should go to the larger post on the "S" post side of the relay(it is a relay not a solenoid, just FYI)
There should be several smaller wires with the battery cable on that post, this post is the power distribution block for the truck.
Starter motor cable goes on the other larger post, this is the ONLY cable on this post.
"S" post is to activate the relay so it will have a smaller wire that comes from ignition switch, it will only have 12volts when key is turn all the way to START on the ignition switch.
It is usually a Red wire with light blue stripe.
"I" post was for older systems, there would be a wire from here to the Coil's + terminal, it would give coil 12volts but only when starter motor was turning.
On older systems the coils wouldn't last very long running on 13.5volts(alternator voltage), so a resistor was added to the coil's + terminal, cutting the voltage to 8volts.
But when starting a cold engine you want hotter spark, as hot as you can get, so the "I" post was used and resistor by-passed when starting engine.
And for the FYI part, a relay and solenoid both use a coiled wire to magnetize a metal core, difference is in what it does.
A Relay is used to pass electrical power, like an on/off switch
A Solenoid is used to move something, a starter motor will often have a solenoid on it, a second smaller cylinder, when activated it pushes the starter gear out to turn flywheel, when deactivated it pulls the gear back, so it moves the gear in and out.
Solenoid is the term often used for fender mounted relay, and pretty much everyone will know what you mean, I did, lol.
Kinda like a "freeze plug", everyone knows what you mean but there is no such thing as a "freeze plug", lol.