I've been dealing with this for a while, i usually stick my foot on the gas pedal a little so people can see that I am turning when stopped.

When i am sitting still, its like the rpm's are too low to power the relay? The turn signals will just stay on (not flashing) unless you rev it a little higher.

Could this be a simple flasher relay? Ive never had this in any other old mopars.....

its in my 71 Challenger