Front turn signal issue

[TKCR]

I have an 86 C10 Silverado. My front yellow marker lights don't work properly with the turn signal. So here's what it does:

With the headlights off:
I use the turn signal left- the right side is blinking.
I use the turn signal to the right-the left side is blinking.

With the headlights on:
Both blinkers work properly to the appropriate side

Everything else works fine the way they should, it's just the front side markers when the headlights are off.