Strangest thing. Front R/turn signal started acting like I had a bulb out. Checked both the front & rear and it seem to show the front buld out. Next morning started to the auto parts store for bulb and it started working.
Check contacts and grounds. Better yet, just redo them all. By that I mean un-plug and re-plug everything in the chain. Take out the bulb, clean contacts. Unplug/replug the socket, then the harnesses etc. Along the way are there any ground wires screwed to body or frame ? Loosen and tighten those too.
Depending on the age of the car intermittant bad connections happen. Also sometimes incandescent bulbs can have a detached filament which then reattaches and the bulb will work again for awhile.