Turn signal help
 

I'm starting to struggle here...usually i'm pretty good with 12v

Turn signals are not working on my truck...but brakes, hazards and parking/running lights all come on. So i have ruled out bulbs, connectors, continuity to each light. The flasher is good, ive tried 3. All work ok on the hazard circuit and none work on the turn circuit.

I replace the turn signal switch, all wires and connections check out like they should; i followed this guide and these diagrams which have been very helpful to truobleshoot and rule evrything out.

Turn and Stop Lamp Diagnosis for 70's Ford Pickup .: Articles

https://www.ford-trucks.com/forums/1...ring-help.html

As soon as i move the turn signal switch to left or right, i lose all power to the blue wire that feeds +12v to the turn signal switch? What am i missing here?

Do you have power to the flasher? If so it must be the wire from the flasher to the turn switch. If not it's probably the fuse, no?

Sounds like the fault is in the switch itself, is this a new switch?

You might have a bad connection in that big plug that the signal harness hooks to under the dash, maybe a socket came loose or something. Worth a try.

Yup, brand new. Its a borg warner brand switch too, so somewhat decent brand quality right?

It has proper continuity on the 4 leads powering the corner lights in signaling positions. The hazards work fine, but as soon as you signal left or right the +12v signal to the blue wire disappears...?

FMC400 will chime in soon (I think) he's our resident electrical guru, he's helped me more than I care to admit, hold steady, he'll be around...

The ford book says to check the feed to the flasher, orange and yellow wire.
Next it says check power to the blue wire (mentioned earlier) If you are losing power here, then it say repair feed from flasher to switch.

Not to come over offensive, but are you sure you are checking the turn signal flasher, and not the 4 way flasher? There are 2 flasher units.

Exactly what I said. Power goes from the TS fuse to the flasher and then to the switch via the blue wire. If there's no power to the blue wire it should be either the fuse, the wire to the flasher, or the wire from the flasher to the switch.

The BLUE wire is the OUTPUT of the flasher, which is a switch that opens and closes. If you turn the signal left or right, the heating element in the flasher heats up until the circuit breaks, and 12 volts will disappear the switch opens. However, as soon as it breaks, it should cool off and close again. If you have an auto-ranging meter, the switch rate may be too fast for you to see 12 volts come and go on the meter. However, the lights should be blinking.

Assuming 12 volts goes away at the BLUE wire for good, this sounds like there is a short downstream in the turn signal wiring. When this happens, the turn signal flasher can act like a thermal fuse. Your turn signal fuse should be preventing this, but if someone has replaced it with the improper rating or wrapped it in foil, you will see stuff like this happen.

Answer these two questions:

1) Is your turn signal flasher getting hot?

2) When voltage at the BLUE wire goes AWAY, what is the voltage on BOTH sides of the turn signal fuse?

Report your results. Don't replace any more parts until you answer all questions clearly and concisely.

thanks for the help, i got it sorted out. the fuse in the block was the wrong spec (SFE), i got fooled because it would read +12V on either side of the fuse but it must have been that it was the wrong size and rating. replaced it with the correct AGW 15A and all is well. again, thanks for keeping me pointed in the right direction...gotta start simple i suppose!

Glad to hear you got it worked out. My guess is that the old fuse was weakly blown, meaning it was intact enough to register 12 volts on either side when unloaded, but fell on it face as soon as you try to run current through it.

yup, thats the same thought i had. should have started there in the first place! thanks again, I really appreciate the help FMC