Are you saying that the brake lights won't come on unless the lights are on? If so, it's misswired. I still think you must be saying brake lights when you mean taillights. No way should the brake lights(or light if it's a stock 1947) have anything to do with the headlight switch. A hot wire goes to the brake light switch and another wire goes from the other terminal on the brake light switch to the tail light assembly. The tail light is wired from the proper terminal on the headlight switch to the tail light assembly. In other words, there should be two wires at the tail light assembly going to different filaments, one the tail light wire and the other the brake light wire.
