i had a custom stereo installed in my bird using the stock speakers, i wanted to upgrade so i took out the worn out dash speakers and replaced them, i also got two alpine 6 1/2 speakers for the doors. When i installed them only one side worked, i took the other side off fixed it, it was just an unplugged connection, but now the other side does not work, it is me off
sounds like you got a ground short,in some of your better decks,,if one speaker is pluged in wrong { pos on neg } you'll lose sound on that bank/side, also check the back ,look for any in-line fuse's,
i persoally run all new wires when installing a head unit, as specially in the older fox cars..