'65 Dart No brake lights. Brake light switch failure?

I thought I had a brain fart LOL. I THOUGHT I knew how these worked. I think the later ones using the separate bulbs was an effort to be "More worldly" or some nonsense. My 98 Ranger had amber separate signals, and when I bought it someone had used one of those aftermarket tow light adapters to convert it back to the combination stop/ signals, and the adapter had gone bad. I got to digging around ???!!!!!???? and here in the cubby was a factory unused tow harness, and the vehicle already had relays, etc to do just that.