You have 2 wires running to the rear now. One operates your left and right tail lights, and one operates your left and right brake lights. Leave the one that operates your tail lights. The one that operates your brake lights will now be used to operate one brake light and one signal light. The splice to the other brake light will need to be cut. Now you will need to run another wire from the dash to the remaining brake light which will also be the signal light on that side.
You have not mentioned what you have for front signal lights. If they are also LED, you will need some special wiring or the signals will not flash. If they are normal filament lights then you will have no problems as you only need one normal light in the circuit for the flasher to operate. This should get you started.
As far as making the teardrops go, just splice into your tail light circuit.
Al
