Tamer on my 68 the tail lights and brake lights are the same inboard bulb in each housing. When the brakes are on it lights up the second element in that bulb. The outboard bulb is the turn signal. I do see green/purple wire going to the housing but think others can help you more with your wiring questions than I can since luckily I have not had to do it
David Barnes
68 E-Type FHC