Continue to Site

Welcome to our site!

Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

  • Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

strange flasher behavior

Not open for further replies.


New Member
I recently bought a used box truck. As I was getting ready to make the purchase, the dealer said they were having trouble with a blown hazard light fuse. They found a non-OEM flasher unit for LED lights installed and so they replaced it with the OEM flasher. This made it work temporarily, but soon the fuse was blown again. I replaced the fuse, but now the flasher is acting funny. All 4 turn signal bulbs (which are controlled by the same flasher as the hazards) are functioning, but they are flashing faster than normal, as if one of the bulbs was burned out. Now when I turn on the hazard switch, they do not light up and the flasher unit (relay type) is rapidly clicking. The 20amp fuse is holding.

I am a little reluctant to replace the flasher without figuring out what happened. The flasher is expensive and if the recently installed one went bad as a result of something else wrong in the system, I'd like to not replace it for the third time.

Does anyone have an idea what this behavior could signify?
Have you physically checked the bulbs, to make sure they aren't LED-type, since the flasher unit was for LED-type lights?
Thermal flashers set the rate with the bulb resistance or even change-in bulb resistance, The hot resistance of the lamp is about 15x the cold resistance.

In a 2000 Impala, for instance, the hazzard switch contains the flasher.
I checked the hazrad/turn signal bulbs and found that they were LED in the rear and incandescent in front. I also tried putting the LED flasher unit back in. It acted the same as the OEM unit. I then replaced the rear bulbs with incandescent ones. The OEM flasher unit is still acting the same. When I turn the hazrads on, it makes a vibrating sound, like it is clicking very rapidly. Can anyone explain the conditions that would cause a relay type flasher to behave this way? Any thoughts on where the problem lies?

Way back when, they had separate flashers for the 4-ways and turn signals. Rapidly flashing could have easily damaged the flasher.
The bulbs themselves cause the flasher to heat up and then change state, The bulbs are a current dependent resistor.

The hazzard switch in some cars is also integrated into the steering column because it interacts with the turn signals.

If you want LEDs, you cant have your cake and eat it too meaning, the lower power thing is out, but the activation time is in. that's why LED brake lights are particularly good.

If you want LED lights, I think you will have to add a resistor in parallel with the LEDs.

In a 2000 impala, i replaced the interior lights with LEDs. In this car, the interior lights auto-dim and auto-bright.

So, what happened. When the ACC circuit timed out, everything went out like it was supposed to. When the trunk was opened the trunk light came on dim. To get the trunk light bright, you had to open and close a door.

Fix, a 3W resistor in parallel with the trunk lamp. It was a #193 bulb if I remember. You need the lamp number. Then find the current. then calculate the resistor and wattage of the resistor and add it in parallel. The LED current can probably be neglected.

I used a panel mount power resistor, but I did not panel mount it.

car wiring diagram of the flasher circuit would not hurt.
IMO, the best thing the OP could do would be to revert the vehicle to the exact factory condition:
Install incandescent bulbs in all 4 corners, and side-repeaters (where fitted), plus a new OEM-specified flasher unit.
Then, and only then, can the system be properly attempted to be diagnosed, should it not work as it was originally designed.
All this after-market crap just creates problems - LED headlamp/side-marker bulbs, supplied by anybody and everybody for a quick buck, tend to play havoc with BCM lamp-failure-monitoring systems, because they do not accurately mimic what the OEM designers expected from an intact, or open, incandescent filament.
That is the setup I currently have, with 4 incandescents and the OEM flasher. Replacing the rear with incandescents did slow down the turn signals. Since the turn signals work normally, I'm assuming that the flasher relay is good. Since both the the LED and OEM relay act the same (rapid fire clicking) when the hazards are switched on, I'm assuming there is a problem elsewhere in the hazard circuit. When the hazards are on, there are no lights at all, not a super fast flashing, just a buzzing from the flasher relay. Is there a condition that would make the flasher buzz like this but not transmit current to the bulbs?
Can you remove and check the hazard light switch for high resistance?
The high flash rate could also be mixed LED and incandescent bulbs in the circuit. I have amber LED clearance lamps on the front of my bike trailer tied to the tail light high beams for signalling, dependent on a working 1157 bulb in that circuit.
Make sure you don't have single filament bulbs where dual filaments -- or vise versa -- are supposed to be. E.g. - 1156 bulbs instead of 1157. Just a long-shot idea...
Not open for further replies.

Latest threads

New Articles From Microcontroller Tips