The left rear turn signal will not blink.

The bulb for the turn signal, emergency flasher, brake light and tail light has 2 filaments. One filament, (the taller one) is for the tail lights. The shorter filament is for the brakes, turn signal and emergency flashers. The emergency flashers work properly for all the other 3 corners of the car. Sometimes I can get the emergency flasher to operate the left rear side. It depends on how I push the emergency flasher down. A slow deliberate push activates the emergency flasher on the left side, as it should. If I then put the left turn signal on and then turn off the emergency flashers the left rear turn signal stays on, as it should. However if I just turn on the left turn signal, without first activating the emergency flasher, the left rear turn signal does not activate. The emergency flashers have to be on when I turn on the left turn signal for the left turn signal to be activated. All the other turn signals (left front, right front and right rear) work properly. Those three bulbs also come on each time I turn on the emergency flashers, as they should. The only problem is the left rear. I replaced the bulb with three bulbs to make sure the problem was not the bulb. I also used those 3 bulbs in the right rear light and they worked fine. It is not the bulb. I used the electric meter to test the left rear and right rear fixtures. They seemed to work properly every time I turned on the turn signal, as they should, with alternating current on and off as activated by the flasher. I also replaced the socket, no change, and flasher, thinking the problem might be the flasher. It did not make a difference that I could tell. However as I said earlier I was only able to activate the left rear turn signal bulb by first activating the emergency flashers, then turning on the left turn signal, and then turning off the emergency flashers. At that point the left rear turn signal was blinking.