Finally solved my turn signal problem on my 67RS after a number of years and wanted to share the solution in case someone else has the same problem.
When I bought my Camaro in high school, 1983, the turn signals didn't work at all. I replaced the flasher plugged into the fuse box and the turn signals flashed although very slowly. This made me a bit nervous but got me through high school.
20+ years later, with the Camaro in storage most of the time due to lack of time or money, it was time to get this fixed once and for all. Of course now they didn't work at all anymore.
Changed the flasher located in the fuse box again, still nothing. Checked and replaced every non working bulb in the car, fixed some loose tail light sockets, still nothing. I read every post on this site and couldn't find anything specific that would solve the problem. Started thinking that it must be the turn signal switch because I couldn't find any ground or short problems so what else could it be?
Well fortunately, have a brother who is an electrician by trade. We broke out every wiring diagram we could find and he started troubleshooting with his voltmeter. Well two hours later we found a second flasher unit underneath the dash that didn't show in any of the wiring diagrams. It is a square, two pronged unit plugged into to a socket underneath the dash just to the right of the steering column. The writing on the flasher says "Signal-Stat 145, 3 Lamp LL". We plugged a new flasher in this plug and a $2 part solved a 25 year old problem and the signals work perfectly.
I'm not sure if this is an RS specific piece but it doesn't show on any diagram I have and I have collected every Camaro book possible over the years.
Hope this helps someone else. Good luck.