Auto Repair Help
Carl’s Corner – Auto Repair Help

By Carl O’Reilly

The turn signals do not flash or they may flash in only one position or one side may remain on constantly with the switch in the off position.

The turn signals use a flasher unit that acts as a repetitive circuit breaker. This unit makes then breaks the electrical circuit that turns on the turn signal bulbs. The cycle will continue as long as the directional switch is turned on. This unit relies on heat build up caused by electrical current flow to determine when to break the circuit. When the switch is initially turned on, electrical current flows through the flasher unit to the bulbs. When this occurs, heat builds up in the flasher unit. When the heat reaches a predetermined temperature, a metal strip within the unit stretches due to the heat and breaks the electrical circuit turning the bulbs off. With the bulbs disconnected from the circuit, the flasher unit cools off. Once it has cooled, the metal strip re-contracts and re-closes the electrical circuit turning the bulbs back on. The usual cause of inoperative turn signals is a defective bulb or flasher unit.

Prior to performing extensive diagnosis, check the vehicles fuses to ensure they are not blown. Some vehicles utilize two fuse boxes, one in the passenger compartment and another under the hood. Consult your owner’s manual for fuse box locations and fuse ratings. If the directionals only flash in one position and are off constantly in the other direction, the usual cause is a burnt-out bulb. When a bulb blows, the current flow in that side of the circuit will be reduced. The reduction in current flow prevents the flasher unit from reaching the needed temperature to switch the bulbs off. Turn the directionals in the position where they are inoperative and perform a visual inspection of the exterior bulbs. Replace any bulbs that are not lit. The flasher unit is used to switch the current on and off for both right and left directionals. If the turn signals are inoperative in both directions, a defective flasher unit or blown fuse is the usual cause. On most vehicles the flasher unit is located on the front or on the back side of the fuse box located in the passenger compartment. Some vehicles use a solid state flasher module that contains transistors and diodes. On these vehicles, you should consult a vehicle specific service manual for proper diagnosis.

You should always use a replacement bulb of the same part number as the one being replaced. Your owner’s manual will indicate the correct bulbs for each location on the vehicle. Using the incorrect bulb can create too slow or rapid turn signal operation. Manufacturers often use grease to repel water from the bulb sockets. Do not remove this grease from the bulb socket when replacing defective bulbs.

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26 Responses to “Diagnose The Turn Signals Dont Work Or Dont Work Properly”

  1. Tony Z says:

    What if the bulb is good the switch was replaced and still no signal lights. What else could be the problem?

    • Anna says:

      I have the same question. Bulb is still good as well as fuse. But still no signal or rear break light

      • artie says:

        I have a 1995 ford f-150 have no brake lights in rear of truck but do have brake light on back of cab of truck, no turn signal lights and no emergency flashing lights, replaced turn signal switch and brake bulbs and fuses and turn signal fuses and do have tail lights, PLEASE help me with out?!!

        • Da-Sarge says:

          With the F150 check the two electrical connectors uner the bed of the truck back by the rear bumper one is round and the other is a square shape these like to carrode rendering the rear lights inoperable also tge tail light sockets can be unplugged from the harness (careful with the clips on eather side of the sockets they like to brake) the tail lights on the 90s and early 2000s (up to current for f250 and higher) they tend to get water in the lights that kills sockets these are the usual causes of the problems if you loose all rear lights check the harness by the chasis in the front drivers side wheel well for chafeing (can also cause rear light loss) very commen on the 1996-2003 F150 all cab and trim types and bed types these are the commin areas to look for failures hope this helps you out

  2. wyatt mohring says:

    right turn signal flashes to fast

  3. shawn says:

    but in new turn signel swicht and have no taillight and blinnkers

  4. Sheila says:

    Signal lights not coming on but hazards do come on. Checked fuses. They seemed to be fine. Please advise. Thanks.

  5. Tommy says:

    Yes you are exactly right! Thank you so much! I changed the flasher and she works fine! $4.00 Thanks to your advice probably saved me up to $400 on mechanics which I’ve seen that many do blow smoke to steal your money. I was thinking I’d have to get someone to pull my steering wheel and change out the tumbler switches! God bless you!

  6. marx says:

    I replaced the flasher on a ford f 150 1998 but still dont work my turn signal stilk dont work

  7. John S says:

    I have a 1995 GMC 1500 4×4. My rear blinkers, brake lights and 4 way flashers do not work, But they all work in the front. My rear running lights work.
    I haves tested all the bulbs they are good, also tested the rear ground wire it is good. Could the problem be my relay under the hood? I am led to believe it controls both the blinkers and the brake lights?

  8. brian v says:

    I have a 76 cheyenne, and i have been having the same problem. My turn signals dont work. But brake light and hazards do i checked the fuses, new flasher, and replaced the turn signal switch but still nothing.

  9. chris w says:

    2006 CVPI no turn signals but when brakes are applied the switch will turn off brake light

  10. jonny says:

    both turn signals will begin rapid flashing, but if I turn the car off and on again both signals begin working perfectly fine.
    This has become more frequent for a few weeks now.
    Saturn ion 2005

  11. Steve says:

    Thanks just got new headlights the blinkers in front didn’t work I got new bulbs with them. Never expected them to be bad but thanks to you I rechecked bulbs and they were bad

  12. al says:

    hello, I just rewired a trailer correctly and the lights function properly. however, the right signal flashes a little fast (trailer connected or not)and the bulbs are flashing on the trailer,but the right blinker seems to to bleed a little into the left light on the trailer only, but not vice-versa. Now that’s strange. What do you think. Thank you.

  13. Gregg says:

    I have a problem I’ve never seen before or heard of. When I put either left or right blinker on ALL lights blink like my hazards are flashing with the turn signal.

  14. tracey-lynn kennedy says:

    just wondering my hazards light works but right and left single doesnt changed fuse and nothing on a 2000 pontiac sunfire thank -you

  15. Matt says:

    For some reason my blinker flashes with the switch in the off position UNTIL I turn my headlights on, that’s the only time it will stop blinking. I do have a blown headlight bulb on the left side, which is also the blinker that is malfunctioning. I’m not sure if the headlight being out is relevant or not seeing as though my blinkers and headlights have separate housings. Anyone offer any advice?

  16. den says:

    There’s a wire going down too your brakes make sure it’s pulled in all the same had the same problem

  17. den says:

    There’s like a relay down there its what makes the clicking noise when you turn on your signal! !!

  18. nandu says:

    Please advise what will be the problem if my Toyota Corolla 2000 car both signal lights are not working. I know that bulbs are fine because it was recently changed.



  19. Stan says:

    I have a 2000 Buick La saber. The left turn signals is acting like it is on double time. The Left rear turn signal lightbulb was out so I replaced it. It still doing The left turn signal double time, with no light on the left rear signal. Next I replace the 15 amp in the fuse box. Still not working right.
    What is your thinking to resolve this problem?

  20. Bob Marshall says:

    Turn signals quit – hazards work. ’99 Olds Aurora.

    Thanks -


  21. vance wright says:

    my left turn will not stop bilking

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