Turn signal in dash won't work

The turn signals all work on the out side but the left turn signal does not light up in the dash cluster.
I have tried to switch the bulbs and switch the plastic plugs the bulbs go into. I also tried fine sand paper on the contact where the bulb twists into.
The car is a 69 dart . I hate driving down the freeway only to notice I have been driving with the blinker on for miles? Maybe I have the stereo to loud? I think a visual might help I'm getting old 47 . Ha Ha I noticed the others person asking about his blinkers and didn't want to steal his post . Thanks