1963Rambler330

I too have a 63 Rambler (American 330 Sedan). 3TBAM Bendix (but using modern radio hidden in the glove box). I just took out the Bendix and replaced the burned out bulb on the dial window. The radio has been unplugged since I got it. Where does the "A" lead originally connect to? Any 12volt source? Would like great to have the light turn on (on the radio) and act like the original is powering the modern speaker/stereo. The info is hard to come by...Thanks!! Lucas