The original taillight should have 4 bulbs (all 1156 or single filament). Which are the turn signal, brake light, taillight and backup light. So what you need to do is to combine your taillight and brake light into one bulb using that 1157 (or double filament) bulb. This way when your lights are on your taillight will brighten when you step on the brake. Just sort out which power wires do those two functions and connect them to your 1157 bulb. Make sure the dimmer light comes on when you turn the lights on, and the brighter one lights when you hit the brakes. I got those two crossed and melted my taillight lenses.
I bought some Mexican taillights for my Super Beetle and they came the same way as your Ford lights, one 1157 and two 1156 bulbs. Long story short, those Mexican lights where terrible and I got a set of Italian reproductions from BFY that are great, and also had the original 4 x 1156 set up.