Sparky's post was very good.
There are actually several factors that determine how you will wire your car, and in your situation, it'd be helpful to know:
What type of kit are you using?
What turn signal switch?
If the brake wire you refer to is the third brake, it will have no bearing on wiring into the tail lights of a stock bodied car. Many aftermarket manufacturers are now incorporating a third brake light wire into their harnesses.
Basically, you should have 4 wires going to the back of the car at a minimum:
Left hand turn & brake (
which should be yellow)
Right hand turn & brake (
which should be dark green)
Running & side marker (
which should be brown) which is common throughout the back of the car
Fuel sending unit wire (
which is tan)
Optional would be the back-up light wiring which is usually light green. Of course, you'd have to make sure to ground the side markers and be sure your tail light bodies have good grounds.