Blue radio wire?

[Russ33]

Hi folk's. I picked up an original am/fm delco radio yesterday. I pulled it out of a 1971 pickup with no windshield. Knobs are a little rusted but do turn. The slider moves but the display does not change. Does it need power for that to work? Also from what I found online the yellow wire off the back is to power. The black/green and green go to speaker. It has a blue wire that comes off from the right side dial. I have no clue what it goes to. I want to put power to it see if it works. Thanks for any help. Russ