I guess you figured out that unplugging beats cutting. If the plastic housing needed swapping, you can release each pin w/ a little screwdriver. Anyway, moving on ...
Since no rear lights are working, I would look at the ground. At some point in the early 1970's, they stopped relying on a sheet-metal screw to ground each lamp and ran a common ground wire to a better screw, at least they did so on the front end (noticed when I used a ~1974 front lamp harness).
