Brake Pedal return spring: 1966 Dodge Dart GT

Are you sure your brake switch is adjusted correctly.

From looking at photos on eBay it looks like the bracket that holds the switch is adjustable. Loosen bolt and rotate the bracket toward the rear of the car.

Not even sure there would have been a OEM return spring. Might have been added by a previous owner, ( my dad did the same thing for the same reason to his 67)