LED Installation Instructions
General instructions on installation of small LEDs
IGNORE THE 1156/1157/3157 etc... Those are if your using LED bulbs already made for your housing, if your doing custom work, just mount the leds as you see above. Its very simple what your doing, your just grounding the positive of the line that goes to your led with a resistor. This make the car think there is a NORMAL bulb still there.
You may not need to do this resistor modification if your only doing the brake/Tail light on certain cars. It depends on the car. But the Turn signal you must do on all cars!