My left turn signal was flashing fast. I checked bulb in back left. Turn signal good but bulb below it was out. I changed that one but turn signal still flashing fast. all other bulbs look good. ??

If the front and rear bulbs flash fast also, replace the hazard switch or you could live with it. As they are working. If one doesn't work, check grounds. I just run a new ground, much easier than cutting open the harness to find the break.

If your turn signal is flashing fast it means the bulb is about to go out and should be replaced soon. You may also have the wrong bulb in or in worst case scenario there is a wiring problem

Most common problem is a bad bulb. Make sure you have replaced the defective bulb with the proper replacement type. Have another look. With the signal light on, make sure both bulbs front and rear come on. If the rear flashes fast then the front bulb will be the problem if it is not flashing at all or vise versa