[Ford blue blood]

Your turn signal switch is the culprit. The same wire is used from the column to the bulb for both brake and turn. The 63 Bird column I installed in my 57 Ranchero had the very same issue. It is a real pain the disassemble the switch while still in the column ( even more of a pain to pull it out of the column ) but look at it real close. It has little springs that will help you learn new vocabulary that help the little switch contacts to make up.