HI Kent & Sally,
I agree with Dick Benjamin. The very 1st thought that I had was the 4-way flasher switch. These switches can be very 'touchy', so jiggle it a few times 1st.
If there's no change, then disconnect it entirely & see if the flashing stops.
My guess is that the 4-way switch is either wholly defective or has almost 40 years worth of "shmutz" ;) built up inside, causing the problem. A good cure is to gently disassemble the switch & use some tuner cleaner (Radio Shack etc) to clean it out. I've done the same with ALL of my P/W,P/L & dash switches & they're good as new!
Let us know what you find.
Carl Falletta, Las Vegas NV '67 CC (ylw)