Signal lights won't blink, simply stay on

i had similar issue (at least with the indicators) with my 71 duster
i have a 69 valiant grille and it has dual filament bulbs in it, one being a turn signal, the other a running light

with the running lights off, the turn signal worked as they should
with the running lights on, the turn signal would NOT do anything, but the turn signal indicator on the dash would turn on and stay on

this only happened to the left side of the car, the right side worked fine
so i looked for visual difference and i notices the right side of the light was properly grounded to the chassis and the left was not

as a test i ran an extra ground wire (just a length of wire with two alligator clips) from the offending light to the battery and that solved the issue