when the headlights are on, the right side blinker doesnt blink on the dash...when the headlights are off, it blinks fine...is it the light bulb or the fuse?

when the headlights are on, the right side blinker doesnt blink on the dash...when the headlights are off, it blinks fine...is it the light bulb or the fuse? Yr and type of car??? Does it blink on the outside? Are all the right side lights lit? Problems like this are grounds, bad connections at the bulbs, or a low voltage problem.