My left hand turn signal suddenly began flashing twice as fast as the right signal. The bulb looks okay. Should I replace the flasher unit and how do I find it?

The flasher is under the dash.If you turn on the signal listen for it's location.Turn on your 4 way flasher and see if the left rear light is flashing.If it's not then replace the bulb.If it still does'nt work after replacing the bulb check if there is power to the socket. Use a probe light.If no power to the socket.There is a break in the wire or worse the signal switch may be the culprit

sounds like one of light bulbs was malfunctioning and caused the flasher unit to blink rapidly and iy burned out. Replace front and rear turn lite bulbs and see if flasher flashes. if not check fuse and replace fuse. If fuse okay replace flasher unit. Good luck

That is a sign of a bad bulb, flashing fast. Check that rear bulb.

Quite a puzzle you have that seems impossible, though such things weren't unusual in the old days of bimetal flasher units. The modern electronic flasher relay is designed to flash at a speed dependent on the amount of current drawn by the circuit so if a bulb goes out the speed doubles or thereabouts, giving the driver an indication something is wrong.
Broadly speaking the flasher unit will operate as it is designed within a current range so if there is too much current flowing or not enough it probably won't work at all.

The turn signal switch is usually a very reliable thing and as the left hand lamps light it is fair to assume it is working ok. If the switch is accessible it would be simple to measure the current being consumed by the circuit, which would be nearly 4 amps with the engine running at a fast idle. If it isn't then I suggest you revisit the lamp grounds and other connections.

My instinct is to suspect the hazard warning switch. It is often an unnecessarily complex switch and wiring arrangement and often responsible for turn signal malfunctions. Mostly operating the switch rapidly for a few minutes puts matters right, though if it doesn't I suggest you check the multiway connector behind the switch.

Has the car been in a fender bender ? check for wiring going to the front and rear lights to see if on has rubbed into a ground wire or the body. ( even if there has been no accident.)

There Is an Electronic Flasher Unit under the dashboard, if you turn on the turn signals and get under the dashboard you will be able to locate it. Unplug the electrical connection from the Flasher Unit and replace it with a new one from your local Auto Parts Store.

The bulb in front is somehow not getting voltage. If memory serves, that headlight assy. has a circuit board of some type, and your problem most likely lies there.

check bulbs

fast flashing on the one bulb is a fault is due to the failure of one bulb, hence the holder for the flasher unit not wirking has gone defective the contact may have broke in the flasher unit not working , look in where the bulb goes and compare the working and non working unit, you may see a contact missing, hence repace unit, or repair

Change the left rear turn signal light bulb. It is probably burnt out! The fast blinking flasher is the clue you have a blown bulb.