Turn indicator light flashes quickly. bulbs fine

was the correct bulb used? this sounds like a single function bulb was used NOT the bulb that will light with the headlights and ALso produce turn singles

Check bulbs first by switching same bulb from other side of vehicle

not enogh infrmation

Yes - the fast flashing is a warning that a bulb is burned out. Change the bulb (be careful to put it in the same as the old one as it probably is 2 bulbs in one , parking and turn/stop) and you should be fine.

The rear left turn signal bulb must be replaced immediatly before it melts the light socket, if it has'nt yet. Also please verify that the correct light bulb is being installed. because even though many bulbs look the same they are not identical. Installing the wrong bulb can be the begining of many, many problems in the particular circuit

Hello. The symptoms you are describing are likely due to a poor ground. Temporarily install a new ground wire by securing a piece of copper wire to the frame with a self tapping screw. Use this ground wire along with the hot wire to see if each of these lights works. If it does, trace the ground wire back to the frame, unscrew it and clean up the metal with emery cloth so you reestablish a good ground.

I believe this car has a rear bulb that has two fillaments, one for side lights the other shared for braking and flash. sounds like a blown bulb or a bad ground connection. Check the bulb and the bulb holder and ground connection.
Turn signal blinking quickly generally indicates a blown bulb front or rear or bad connection.

Bad earth connection.Clean or replce wire.

Check correct wattage globe is installed in both front and rear indicator lights;
check if any other side/repeat indicator lights have failed.

Check if you have fire at the centre pin of the light socket using a tester. If not, the wiring is shot somewhere. If you have fire, you replaced the dud bulb with another dud! (I know, it happened to me some time ago on my Chevy)