Yes, that the Throttle Position Solenoid. Looking through my 1975 Service Manual provided plenty of info about it.
The condensed version that it is part of the catalytic converter protection effort. It's job is to hold the idle at 1500 rpm under certain circumstances to keep the converter from overheating, presumably from excess fuel.
To answer your question of what it connects to, the answer is a small metal box called the Electronic Speed Switch. Luckily I had a '75 and that box should be found on the passenger side inner fender somewhere. I think there are two metal boxes there in fact.
One will have two wires...that is the voltage regulator. The other is the speed switch and will have three wires, assuming it's still there.
Of the three wires at the speed switch, one goes to one side of the ballast resistor, one goes to the other side of the resistor and the third is your mystery wire you can't find yet going to the Throttle Solenoid.
Depending on whether you have everything still there, you can re-connect it as original, leave it as-is or remove everything, especially if you have no converter anymore.
