72 Demon playing the juice harp and brake light misery

My best guess for the noise ( if only when wipers are running ) is wiper linkage. We've seen pics of cases where someone had replaced the proper bushing with nothing more than a retainer clip of some sort. Result is metal to metal movement and lost motion.
The turn signal switch should send brake lamp current ( from white ) back out on 2 wires when its in centered position, when the brake lamp switch is closed. The switch changes the current path to one brake and one rear turn when activated for left or right turn.