[68c10airstream]

It's been more years than i care to remember but the horn contact plastic piece you need could be called a turn signal cancel cam. Does the under side of the white plate have a couple of high points or wings 180 degrees apart?? If so than that is what it is. As you turn a corner with the turn signal on, when you straighten out the steering wheel this white plate with the wings raises the signal switch latch and it returns to center (turn signal flasher off).