Idle Stop Solenoid?

[1972Blaze]

What was the purpose of the idle stop solenoid for my 1972? Was it used specifically on vehicles equipped a certain way or were they put on all trucks? My truck has A/C and it will not stay running without adjusting the idle way up when the A/C is on. I had an Edelbrock carb (no idle up that I can identify) and replaced it with an original Quadrajet, but it had no idle up solenoid. If I put one on and it works properly will it idle the engine up when the A/C is on? What causes the solenoid to engage? What does the wire to the solenoid look like? I have a green with white stripe wire loose that I suspect may be the right wire. Any help is appreciated.