[Tommy]

Dlotz,
A double filament bulb requires three connections: 1) the ground serves both filaments; 2) one wire with 12v illuminates the brighter filament for brakes and/or turn signals; 3) one wire with 12v illuminates the dimmer filament for running/parking lights. If you car is equipped with a brake/turn signal system, you can have the bright filaments in all four rear bulbs serve as both brake and turn signal lights. If you car, like mine, is not so equipped, you can run your turn signal wires to the bright filaments on one bulb on each side, and the brake light wires to the bright filaments on the other bulbs on each side.