had the same exact problem on my 68 dart ......it turned out to be the turn signal switch in the column on mine.......one way to confirm that is disconnect the clolumn wire connector and apply power to the terminal ....on mine it was a tan wire to right side and when i did that it worked the way its supposed to .
if yours is same problem then your dash indicator isnt working.....but if you apply power to the terminal it will.