Why are my rear turn signals acting as hazard flashers when I signal a turn? The front turn signals work fine but the rear ones always flash simultaneously as if I had turned on the hazard flashers. Recently wired a stereo. Could this be the cause?

How do I know if my flasher relay is bad?

Symptom of a bad or failing turn signal / hazard flasher is hazards or turn signal lights that do not function. If the flasher breaks or has any internal issues it can cause the lights to malfunction, or not respond at all when the turn signal lever or hazard light button are pressed.
Jan 19, 2016

Symptoms of a Bad or Failing Hazard / Turn Signal Flasher - YourMechanic

For the cost involved, I would change it.

https://www.fixya.com/cars/t24552531-flasher_turn_signal_located

https://www.google.com/search?q=2011+kia+sorento+flasher+relay

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Lamp, bulb, supply and ground obviously ok as the hazards work - I suspect the hazard switch might be faulty or something like a dodgy multiway connector onto the switch...

What fuse are you pulling ?

Hazard Lamps
The hazard warning switch is part of the turn signal switch. The turn signal switch receives battery voltage at all times through the HAZARD SWITCH Fuse. When the hazard switch is placed in the HAZARD position, battery voltage is applied to the hazard lamp/turn signal lamp flasher. The hazard lamp/turn signal lamp flasher sends a turn signal flasher signal to the turn signal switch. The turn signal switch provides all of the turn lamps and turn indicators with the turn signal flasher signal, simultaneously flashing them on and off.

Turn Signal Lamps
The front turn signal lamps are made up of the front park/turn signal lamps and rear turn signal lamps. The front turn signal lamps flash with the rear turn signal lamps when a turn is initiated using the turn signal/multifunction lever. The turn signals will operate only with the ignition switch in the RUN position and will not operate during hazard flasher operation.
When the ignition is turned to the RUN position, battery voltage is supplied to the TURN SIGNAL Fuse. Battery voltage is then applied through the turn signal fuse circuit to the turn signal switch. When the turn signal switch is placed in the LH or RH position, voltage is supplied to the hazard lamp/turn signal lamp flasher. The hazard lamp/turn signal lamp flasher supplies a turn signal flasher signal to the turn signal switch. With the turn signal switch in the LH or RH position the corresponding turn signal indicator, rear turn signal, and front turn signal receive the turn signal switch signal and will flash. The front turn signals receive the turn signal switch signal from the turn signal switch via the BCM. The turn lamps are permanently grounded.

Replace the turn signal switch. Refer to Multifunction, Turn Signal, and Hazard Switch Replacement - On Vehicle in Steering Wheel and Column - Tilt.

I would replace the turn signal hazard combo switch.

Hi there., when flashers/indicators work rapidly on the dashboard you should check whether it is the same on the actual bulds. Fadt flashing is usually a sign of a bulb failure somewhere. If everything is functioning ok externally I would consult a competent technician for a diagnosis.

Have you checked the bulbs already?
Don't know what kind of car you are dealing with here.
Most vehicles - the brake lights and rear turn signals share the same electrical circuit to the rear tailights. Usually the turn signal switch will separate which signal goes to the back.
Do your brake lights work? Is there a High mounted stop lamp and does it work?
I have seen a Hazard Switch be ON and fuse blown causing the Hazard Flasher to be inop - which prevented the turn signals from working. Turning OFF the hazard flasher brought back the T/S.
Check the rest of the lights - see what does and doesn't work - and do the front turn signals flash? Stay On? Or flash really slow?
Let me know what you find out and if this helps you at all.

The wire feeding the front left turn signal is likely crimped or stretched and touching the body somewhere. Do you best to trace the left front turnsignal wire back as far as you can - even just jiggling it might give you short term solution (although it will probably come back).
The fast flash of the rear light is because the short up front is letting too much electricity run through the flasher module. This makes it run too fast. Find the short up front, and both problems will be solved.

YOU MIGHT HAVE A BURNT OUT RELAY IN FUSE COMPART UNDER YOU CARS HOOD CHECK THAT OUT THRU YOUR CARS MANUAL,IT WILL SHOW YOU WHICH RELAY IT IS?

all gm cars and most others have two flahers one turn signal and one hazard check behind the fuse box for the other flasher

Yes, the problem is the turn signal flasher is defective. You can has two flasher relays. One for the turn signals and one for the hazard lights. That is why the hazard lights flash and the turn signals do not. Replace the turn signal flasher relay located on the drivers side of the steering column, mounted behind the instrument cluster in the convenience center. They are both mounted in the same location so turn on the hazard lights and the one that you put your finger on that is not clicking is the turn signal relay.