Just got a Delco radio that came out of a 68 Camaro in the mail today. Its going in a 67 Camaro. Need some help with the connections. In the back of the radio there is a 3 plug connection, but the connection coming from my car only only has 2 wires going in to it (black and green). There is a third connection there, but there isn't a wire running to it. There is another yellow wire which im assumming goes to the radio. Did someone just change the connection on the yellow wire? See attached pics. Thanks for the help.