Turn signal issues
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7th Gear
Joined: Sep 2021
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Turn signal issues
I just bought a '85 F350 w/ 6.9 diesel. I changed the front and rear turn signals and headlights to LED. I've installed resistors on both. I've changed the flasher and the hazard flasher to electronic. I've added a ground to the headlight socket ground. After all this, my turn signals don't work when I turn the headlights on. Any suggestions??
FTE Legend
Joined: Nov 2015
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From: Angier, NC
That is a strange one as the 2 systems are not connected in any way that I have seen over theyears.
On the head lights why did you add a 2nd ground as each side has its own ground from the light sockets to the body.
Maybe that other ground you added you tied into the turn signal side of the systems?
I would remove that 2nd head light grounds and see what happens.
If the dose not work it would be time to put the non-LED bulbs back in for the turn / brake lights and see if they work with the head lights on.
If still not then put the old head lights back in and test again if the lights work as they should.
If not then you will need to figure out why. Again the 2 systems are not tied together so I dont know why it would be happening?
Now if the normal head lights and all works then install the LED turn /stop bulbs and run your test and see what happens.
If working then try the LED head lights and if not working the LED head lights are the cause but again I cant see how?
Dave ----
On the head lights why did you add a 2nd ground as each side has its own ground from the light sockets to the body.
Maybe that other ground you added you tied into the turn signal side of the systems?
I would remove that 2nd head light grounds and see what happens.
If the dose not work it would be time to put the non-LED bulbs back in for the turn / brake lights and see if they work with the head lights on.
If still not then put the old head lights back in and test again if the lights work as they should.
If not then you will need to figure out why. Again the 2 systems are not tied together so I dont know why it would be happening?
Now if the normal head lights and all works then install the LED turn /stop bulbs and run your test and see what happens.
If working then try the LED head lights and if not working the LED head lights are the cause but again I cant see how?
Dave ----
Lead Driver
Joined: Nov 2013
Posts: 7,163
Likes: 1,170
The $64,000 Question:
Did the turn signals work before converting to LED?
Also, exactly what happens when you say the turn signals don't work? Do the lights illuminated steadily without flashing? Or do they just stay completely off?
Do you still have the old bulbs? I'm curious if everything works if you reinstall them.
This troubleshooting guide should help:
https://www.ford-trucks.com/forums/1...ing-guide.html
Specifically, for troubleshooting I HIGHLY recommend replacing each flasher unit with a jumper. This make the circuit much simpler and easier to check for power and ground.
FTE Legend
Joined: Nov 2015
Posts: 30,880
Likes: 4,117
From: Angier, NC
The $64,000 Question:
Did the turn signals work before converting to LED?
Also, exactly what happens when you say the turn signals don't work? Do the lights illuminated steadily without flashing? Or do they just stay completely off?
Do you still have the old bulbs? I'm curious if everything works if you reinstall them.
This troubleshooting guide should help:
https://www.ford-trucks.com/forums/1...ing-guide.html
Specifically, for troubleshooting I HIGHLY recommend replacing each flasher unit with a jumper. This make the circuit much simpler and easier to check for power and ground.
Did the turn signals work before converting to LED?
Also, exactly what happens when you say the turn signals don't work? Do the lights illuminated steadily without flashing? Or do they just stay completely off?
Do you still have the old bulbs? I'm curious if everything works if you reinstall them.
This troubleshooting guide should help:
https://www.ford-trucks.com/forums/1...ing-guide.html
Specifically, for troubleshooting I HIGHLY recommend replacing each flasher unit with a jumper. This make the circuit much simpler and easier to check for power and ground.
Kind of why I had him putting the old bulbs in for testing.
Dave ----
Lead Driver
Joined: Nov 2013
Posts: 7,163
Likes: 1,170
G801 is located in the same general area on the left side.
These grounds attach to the inner fenders, which are marginal ground paths at best. When I was writing that troubleshooting guide, I disconnected G801 just for giggles. This caused the right headlight to flash dimly with the turn signals.
FTE Legend
Joined: Nov 2015
Posts: 30,880
Likes: 4,117
From: Angier, NC
Well there you go I was not as right (I did not say wrong) 
I knew of that ground wire on both sides I just did not remember that the 2 systems share the same ground wire through the harness.
Dave ----
I knew of that ground wire on both sides I just did not remember that the 2 systems share the same ground wire through the harness.
Dave ----
Lead Driver
Joined: Nov 2013
Posts: 7,163
Likes: 1,170
Dave, Dave, Dave...
There's no shame or need to hesitate admitting when you're wrong. I mean, just look at me. I never hesitate to point out when you're wrong. It's very cathartic.
There's no shame or need to hesitate admitting when you're wrong. I mean, just look at me. I never hesitate to point out when you're wrong. It's very cathartic.
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Thread Starter
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7th Gear
Joined: Sep 2021
Posts: 7
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That is a strange one as the 2 systems are not connected in any way that I have seen over theyears.
On the head lights why did you add a 2nd ground as each side has its own ground from the light sockets to the body.
Maybe that other ground you added you tied into the turn signal side of the systems?
I would remove that 2nd head light grounds and see what happens.
If the dose not work it would be time to put the non-LED bulbs back in for the turn / brake lights and see if they work with the head lights on.
If still not then put the old head lights back in and test again if the lights work as they should.
If not then you will need to figure out why. Again the 2 systems are not tied together so I dont know why it would be happening?
Now if the normal head lights and all works then install the LED turn /stop bulbs and run your test and see what happens.
If working then try the LED head lights and if not working the LED head lights are the cause but again I cant see how?
Dave ----
On the head lights why did you add a 2nd ground as each side has its own ground from the light sockets to the body.
Maybe that other ground you added you tied into the turn signal side of the systems?
I would remove that 2nd head light grounds and see what happens.
If the dose not work it would be time to put the non-LED bulbs back in for the turn / brake lights and see if they work with the head lights on.
If still not then put the old head lights back in and test again if the lights work as they should.
If not then you will need to figure out why. Again the 2 systems are not tied together so I dont know why it would be happening?
Now if the normal head lights and all works then install the LED turn /stop bulbs and run your test and see what happens.
If working then try the LED head lights and if not working the LED head lights are the cause but again I cant see how?
Dave ----
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Thread Starter
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7th Gear
Joined: Sep 2021
Posts: 7
Likes: 0
That is a strange one as the 2 systems are not connected in any way that I have seen over theyears.
On the head lights why did you add a 2nd ground as each side has its own ground from the light sockets to the body.
Maybe that other ground you added you tied into the turn signal side of the systems?
I would remove that 2nd head light grounds and see what happens.
If the dose not work it would be time to put the non-LED bulbs back in for the turn / brake lights and see if they work with the head lights on.
If still not then put the old head lights back in and test again if the lights work as they should.
If not then you will need to figure out why. Again the 2 systems are not tied together so I dont know why it would be happening?
Now if the normal head lights and all works then install the LED turn /stop bulbs and run your test and see what happens.
If working then try the LED head lights and if not working the LED head lights are the cause but again I cant see how?
Dave ----
On the head lights why did you add a 2nd ground as each side has its own ground from the light sockets to the body.
Maybe that other ground you added you tied into the turn signal side of the systems?
I would remove that 2nd head light grounds and see what happens.
If the dose not work it would be time to put the non-LED bulbs back in for the turn / brake lights and see if they work with the head lights on.
If still not then put the old head lights back in and test again if the lights work as they should.
If not then you will need to figure out why. Again the 2 systems are not tied together so I dont know why it would be happening?
Now if the normal head lights and all works then install the LED turn /stop bulbs and run your test and see what happens.
If working then try the LED head lights and if not working the LED head lights are the cause but again I cant see how?
Dave ----
The $64,000 Question:
Did the turn signals work before converting to LED?
Also, exactly what happens when you say the turn signals don't work? Do the lights illuminated steadily without flashing? Or do they just stay completely off?
Do you still have the old bulbs? I'm curious if everything works if you reinstall them.
This troubleshooting guide should help:
https://www.ford-trucks.com/forums/1...ing-guide.html
Specifically, for troubleshooting I HIGHLY recommend replacing each flasher unit with a jumper. This make the circuit much simpler and easier to check for power and ground.
Did the turn signals work before converting to LED?
Also, exactly what happens when you say the turn signals don't work? Do the lights illuminated steadily without flashing? Or do they just stay completely off?
Do you still have the old bulbs? I'm curious if everything works if you reinstall them.
This troubleshooting guide should help:
https://www.ford-trucks.com/forums/1...ing-guide.html
Specifically, for troubleshooting I HIGHLY recommend replacing each flasher unit with a jumper. This make the circuit much simpler and easier to check for power and ground.
Lead Driver
Joined: Nov 2013
Posts: 7,163
Likes: 1,170
I missed this little tidbit. Did the bulb manufacturer say this was required? AFAIK, nearly all LED turn signal bulbs sold today have internal resistors. This mimics the electrical characteristics of incandescent bulbs, so the LEDs will be plug ‘n play.
When automotive LEDs first came on the market, they were fairly primitive and required external resistors. But I don’t think that applies today.
FTE Legend
Joined: Nov 2015
Posts: 30,880
Likes: 4,117
From: Angier, NC
Dave ----
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7th Gear
Joined: Sep 2021
Posts: 7
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I missed this little tidbit. Did the bulb manufacturer say this was required? AFAIK, nearly all LED turn signal bulbs sold today have internal resistors. This mimics the electrical characteristics of incandescent bulbs, so the LEDs will be plug ‘n play.
When automotive LEDs first came on the market, they were fairly primitive and required external resistors. But I don’t think that applies today.
When automotive LEDs first came on the market, they were fairly primitive and required external resistors. But I don’t think that applies today.
Lead Driver
Joined: Nov 2013
Posts: 7,163
Likes: 1,170
What brand and part number LED turn signals did you install? I'd like to see the specs and whether the resistors are really needed, or if they are masking some other fault.
In the meantime, look at grounds G801 and G801, as seen in post #5 in this thread. I suspect they are not making a good connection all the way back to the battery. The easiest way to test this is to connect a test jumper between the wire terminal and the battery's negative post. See if that helps.
Also, have you tried replacing the flasher units with a solid jumper for troubleshooting? I'm curious if your LEDs illuminate properly with the flasher units out of the circuit.
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