Left blinker not working when headlights are on.

[8GMC6]

Hello all! I recently purchased a 86 GMC K2500 to work on and learn more about vehicles. With that being said I really don’t know much about how to fix electrical issues. Here is my problem…
My blinkers work normally during the day but once I turn on my headlights my left blinker doesn’t work and my right blinker works very slowly.

 

[fast 99]

Could be voltage or lack thereof, grounds or flasher itself.

 

[Wallace6]

I Had the same problem and the front bulbs fixed it. Good luck

 

[Ricko1966]

Make sure someone didn't put single filament bulbs into dual element sockets.

 

[Wallace6]

It actually ended up being a slightly bad ground

 

[sidschev]

did you add some blinker fluid

 

[roger0080]

If you're in the rust belt, this would be common on my 72's and I finally soldered a ground wire onto the socket itself and ground that wire on all my signals and have not had a problem since. HTH.