My left rear blinker is not working, but the right one does. Car is a 66 mustang coupe. From looking at the wiring diagram, the right and left blinkers come off the same switch, go through the same plugs, etc., all the way to the back of the car. Would I be correct in assuming that since my right blinker works, the problem has to be where the left blinker wire connects to the housing? Yes, bulbs have been replaced.

 

Try wiggling the boot that goes to the tail light bucket.

I fought with those for many many years. I finally go so sick of them that I found a company that made LED tail lights the DONT utilize the original connector. I got to beat the old connector out of the tail light bucket with a hammer...it was quite satisfying.

If wiggling the boot doesnt work and both brake lights work. Its likley the wire on the turn signal switch is broken this requires pulling the steering wheel to investigate...really not that hard.

 

Usually, but not always, a bad ground connection. imp

 

Is it just the blinker that doesn't work? Do your running lights & brake lights work?

 

Here is a diagram of the turn signals. Does the dash light come on? Does it work with the emergency flashers?