When I was a lowly engineering coop student at GM, I actually built one of these things from scratch. Unfortunately, I did not have much money, and I did not own a T/A. So what did I do? I put it on my '74 Plymouth Valient. I still remember the circuit well. I used a TTL 74154 4/16 line decoder which fed sixteen power transistors that drove the sixteen turn signal lamps. The array of lights was about 16" long, and I mounted them on a piece of wood. The circuit itself was mounted in a plastic box that was sealed to keep water out. I mounted the whole thing behind the grille of my Valient, so it was completely hidden durning the day. But at night - it was quite cool.
I had plans to modify the circuit to use the engine RPM to clock the TTL circuit, thus the "scanning" of the lights would follow the RPM of the motor. However, I sold the car (with the circuit) before this mod could be done. I remember bringing in the circuit to GM's vehicle engineering center and showing it to a couple of engineers - got a few laughs and pats on the back. This actually inspired another student to have built (on GM time) a much more professional looking version that he put in his Camaro.
Nice thread - brings back a lot of memories.
