Interchanging tail lights when signaling?

I know exactly what you are trying to do!!    There are electronic modules that replace the old mechanical alternating turn signal components made for the 60's model T-Birds, 67 and up Cougars, and the late 60's Mustang Cobra's. Not sure how you would go about using one of these for your application, but figured this might help to lead you in the right direction. I have never actually used one of these modules, but the only thing is that the cars above had 3 tail lights per side, not sure how it would work with only two lights. Well, hopefully this will help

http://www.squarebirds.org/sequential.htm

http://www.imperialclub.com/Repair/Year/1969/Seq/conversion.htm

What is the circuit inside the STS1 module?  How do I prevent feedback from this circuit diagram to the original car wiring if I want to apply your diagram to my separate stop lamps and turn signal lamps, not to two or three separate stop lamps as shown?