No turn signals, no short, good fuses, one cranium ache!

[tonyjunior]

I've searched this forum several times, but please forgive me if this issue is already resolved and I just missed something. Here is my issue:

I have a 1977 F-350 dump truck. The turn signals just quit working one day. The flashers work flawlessly, and the fuses are all good. I double checked with a continuity tester. I get power to the brand new flasher and I'm not sure how to check the power in the fuse panel itself. The dash indicators don't work nor did any signals. They don't light up and stay on either. I've read that the reverse lights and the signals are on the same fuse. I don't have either. I'm having a hard time wrapping me head around how the turn signal system works which is weird because i'm usually circuit capable. Can anyone explain to me the path of the current or tell me how to check what i haven't checked so far? I'm at a loss, but i'm certain there's an old school ford fanatic mechanic on here that knows these systems like the back of their busted knuckles!

Thanks!
TJ

 

[DNFXDLI]

This is for a 79, but the wiring is basically the same, refer to pages 20-22 of this manual:

http://www.fordtruckfanatics.com/forum/showthread.php?t=29167

Welcome to the site!

 

[tonyjunior]

OK. awesome. lots of information there. thank you! I look at the diagram and i'm still confused on where the power goes. does it come from the battery, through the fuse box, up the column to the switch, back down to the flasher then to the dash indicator and ext. lights? there are only two wires on the flasher and they aren't a positive and negative that's for sure. I'm going to study that diagram.

 

[DNFXDLI]

The flasher has a heating element in it (a resistor)...which heats up and moves a contact....there is no positive or negative....think of it as an automatic switch.

Yes to what you said on the power route.

 

[tonyjunior]

I have 13.xx volts on the black side of the resistor harness when the right turn is on, i have similar voltage on the reddish side of the harness in left turn. it's not kicking in and out (flashing). Would that lead one to believe that there is a bad ground AFTER the thermal flasher since it's not heating up and "flashing" since it takes a ground to create heat? that could be in a large number of places, correct? I'm really not trying to be dense or difficult, i really enjoy tracking and learning electrical issues and resolutions!

 

[DNFXDLI]

I went back and re-read that schematic....the power goes through the flasher first, then to the switch, then to the lamp...so what you need to do is identify the wire and use a tester (light bulb type) and follow the wires.

The ground completes the circuit...so yes, you need the ground.

 

[Jssec]

On my 78 F350 front turn signals the ground tab on the sockets that holds the light bulb were rusted into. Wire to socket was grounded but when I checked for a ground inside socket on spring tab had none. When I removed the foam gasket from the white light socket I could see the ground tab was rusted completely into about drove me nuts till I found it.

 

[tonyjunior]

AHHH yes. That changes everything AND makes more sense from what i'm seeing on the voltmeter. I suppose it's going to be best to go ahead and pull the wheel to be able to completely track all the wires. wish me luck! Unless I have more questions, which is likely, i'll post my findings and fixes.

 

[tonyjunior]

Jssec - Did you have the same symptoms I do? Hazards work but not dash indicators or turn signals anywhere? That's interesting a bulb socket could kill em all!

 

[DNFXDLI]

The socket suggestion is a good one as they do rust.

I'm not sure if that is it in this case as it looks like both the dash indicator and the turn signal lamp come off the same terminal of the turn signal switch...so if both are not working, it could be the switch itself....it could also be the grounds on both though....and this might sound elementary, but you have checked the lamps in the dash and turn signal?

 

[Fellro]

Turn signals should only have power with the key on, while hazards are battery powered.

 

[tonyjunior]

I have checked the bulbs themselves. The hazards work flawlessly. The exterior lights all flash and the dash indicator lights flash. it's only the turn signals that are throwing me problems. This wiring is almost 40 years old so anything is possible!

 

[tonyjunior]

Fellro= Are you suggesting that it may be in the ignition switch specifically on the ACC.? I tried with switch in accessory and with the truck running. They just out of the blue quit working all together. tantalizing nonetheless.

 

[Fellro]

If there is no power supply, then it is possible to be in the ignition switch, but I have not reviewed the harness diagram to see if there are other common circuits to go as well. I do not believe the turn signal has a specific terminal from the ignition switch itself, but was merely making sure you were aware that the key must be in the run position to activate the turn signals for testing. They will not work in the acc position. There is a fuse that applies to the turn signal itself. That was my other point, just because the hazards flash does not mean that the turn signals should. Different power supplies.

 

[tonyjunior]

Copy that. I double checked with it running just to be sure without a doubt that there should be power going to the signals. This has me stumped. I'll pick the tools up tomorrow to remove the steering wheel and take a gander at the switch and possibly follow every inch of the wires to see where it fails. Keep the information coming!!

 

[Mil1ion]

Everything runs through the TS switch.
Have you checked power on TS side of fuse for power with key in run/acc?

 

[BKW]

THREE different T/S switches for 1973/77 F100/350's, make sure if planning to replace it, that you buy the correct switch.

There are TWO flashers, one for the T/S's another for the 4 ways.

 

[BigNate]

THREE different T/S switches for 1973/77 F100/350's, make sure if planning to replace it, that you buy the correct switch.

There are TWO flashers, one for the T/S's another for the 4 ways.

My sons gave us fits. There were ground issues on the right side, and the TS flasher was bad. We had to replace a front turn socket, replace a ground wire, and the flasher of course.