forgive me if this topic has been covered. first of all im not a ford guy, forgive me for my ignorance.
so that being said, i am working on my father in laws 77 f something dump/flatbed. the left turn signal doesnt work at times. here is what i have done and found:
- traced wiring back to first 4 pin connector uncovering wire from misc. tape and loom looking for breaks (found none)
- pulled apart connector and checked for corrosion, cleaned corrosion.
- replaced all butt connectors with new clean seal a crimp connectors.
- checked for power with probe at wires on socket ( i know its improper but i pierced the wires right behind the light recepticle inside the black rubber, found power)
- swapped around the two flasher relays under the dash (made no difference)


so i just tried the 4 ways/hazards and all turns lit up. i turned them off and tried left turn again, nothing. so i hit the 4 ways and while the 4 ways were on i put the left turn on then turned off the 4 ways. it worked. why? this is the only way i can get the left turn to work is by tricking it into working with the 4 ways. does this mean i have a bad relay or is there something that controls the turn in conjunction with the 4 ways? what is the bad part here?

 

I'd say you have a bad turn signal switch.

 

I agree with HIO Silver The 4 ways are a different circuit. I had one that you turn it on and then tap it worked but you had to tap it! there old and cranky sounds like its asking for a new switch.