I have a similar problem. All my lights work correctly except when I step on the brake my left front running light also lights up. It still works as a running light and turn signal. I will check the ground on the brake lights.
1972 with a lot of later year parts (F2, 4spd, Disc in front, Pw steering, AC, Procar bucket seats) and death wobble! I got to get to work on it again.