Emergency flashers

My '68 factory manual says that, "all turn signal lights and the turn signal indicators flash simultaneously."

It also says that the turn signal switch should be in the neutral position, "to prevent a characteristic feed back through the accessory circuit causing intermittent operation of the accessories."

Also, "When the flasher is operating, application of the brake pedal will override the system and interrupt the flasher. All lights will remain on bright until the brake pedal is released."