My daughter’s 1987 Pontiac Bonneville with 45,000 miles (yes, 45 thousand miles) has a weird turn signal problem. The right turn signal was not working, so I found the bulb that seemed to be out (one in the rear) and replaced it. Signal worked fine for a day or so, then my daughter reported the right turn signal was not working again. I went out and looked, and sure enough the same rear bulb was out. I started to remove the lens, and my younger son came out wanting to know what I was doing. I wanted to give him an opportunity to learn a little about cars, so for a demonstration I told him to go look at the rear turn signal lamps while I engaged the turn signals. Well, wouldn’t you know it, the right turn signal, as well as the left, worked fine. 
I oput eerything back together, we tried it several more times, and it still worked fine. I tried it the next day, and it worked fine.
My daughter got in the car the following day to go to work, and she said the right turn signal did not work. I checked it, and indeed it seems to not be working. Bottom line, sometimes it works, sometimes not.
So – what could it be? The switch on the steering column? The wiring? Both? Neither?What to check next and how?
There may be a faulty ground connection to the rear light causing this. The flasher unit may be the cause also. If the right front light at least turns on when the problem occurs I would say the switch is ok.
I would first replace the bulb with another one. You may have gotten a defective bulb. Sometimes bulbs have a loose filament and will work temporarily after they are jiggled.