[Sparky]

A Nova Rear Taillight shares the Brake Light/Turn Signal Circuit. The Brake Light wire comes off the Brake Switch (White wire) and goes to the Turn Signal Switch in the Steering Column, through the Turn Signal Switch and out to the Taillights via the Yellow Wire (Left Turn/Brake) and Dark Green (Right Turn/ Brake).
When you have the Brakes applied and Turn on the Turn Signal. The Turn Signal Switch cancels the Brake Light circuit and engages the Turn Signal circuit through the same Yellow and/or Green wire depending if it’s the Left or Right Turn Signal that you turn on.
With the two wires that you have coming out of your taillight socket, one of them will be a Brake/Turn Signal and the other will be a Taillight or Run Light, the socket finds ground through the Taillight assembly.

I hope this helps,
Sparky