77 corvette, all lights work but on rear how many lights are suppossed to light up when brake is applied?

I have a 78 Corvette and only the outer lights are tail and brake lights.The inner are backup and a reflector.

just the 2 out side tail lights work as brake lights the 2 inner lights are your running lights or just tail lights no dual purpose bulb here.tail light number for out side is 1157 dual purpose bulb,and the inside light is a 1156 single purpose bulb.