Let me start off by saying I'm not the greatest with wiring, and I'm not sure whats going on with my 91.

What I know is...the right blinker works fine and all of the hazard lights work fine. When you turn on the left blinker it and the marker light lights up, but does not blink. Any suggestions?

 

Have you checked the blinker fluid lately?














Just kidding, actually this EXACT same thing happened to me except it was on the right side when we bought the truck, and i turned out to be a bad flasher believe it or not.

Does it flash in the cab (on the cluster) ? Or does the green arrow light up and stay lit?

If it flashes on the gauge cluster that means the flasher is good and possibly the 2nd element of the front left marker light bulb is bad and bulb needs replacing. it's an 1157a bulb

 

The arrow on the cluster stays lit and does not blink, but it does blink when I turn on my hazards. The bulb isn't burnt out because it works with the hazards, but maybe it's bad??

Did I mention I hate electrical problems?

 

Could be a bad bulb or the flasher like Brandon said. When you turn the blinker on and it just stays lit go look at the lights on the truck and see if they are both lit.

 

I'd replace the bulb and the turn signal flasher.

sounds like the flasher is bad

 

Check the bulb. Even though it may not be blown, the ends on the bulb may be worn down mot making contact enough to blink. That is what happened with mine. A new bulb corrected that

 

You might start looking at grounds and for corrosion. One check to make turn your for ways on and look at both front and both the rear to make sure that they are blinking at the same time not opposite one another. If one of them is opposite the other one of them has a background. Good luck.

 

Whenever I have strange electrical problems the 1st 3 things I do are:
1-Check the grounds
2-Double check the grounds
3-Recheck the grounds
That being said the flasher and bulbs are cheap and I would replace them plus it does not hurt to have spares for the glovebox if they are not the problem.